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CHEMISTRY 

OF 

FOOD   AND    NUTRITION 


THE  MACMILLAN  COMPANY 

NEW  YORK    •    BOSTON   •    CHICAGO 
SAN    FRANCISCO 

MACMILLAN  &  CO.,  Limited 

LONDON  •  BOMBAY  •  CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  Ltd. 

TORONTO 


1 


CHEMISTRY 


OF 


FOOD  AND  NUTRITION 


BY 
HENRY   C.    SHERMAN,   Ph.D. 

PROFESSOR   IN    COLUMBIA   UNIVERSITY 


i     '      * 


'Ntia  gork 

THE   MACMILLAN   COMPANY 

1912 

AU  rights  reserved 


Copyright.  1911^ 
By  the  xMACMILLAN   COMPANY. 


Set  up  and  electrotyped.     Published  February,  1911,     Reprinted 
October,  1911 ;  March,  October,  1912. 


NoriDooli  iPress 

J.  S.  Cashing  Co.  —  Berwick  &  Smith  Co. 

Norwood,  Mass.,  U.S.A. 


S6 


SIOLCKiY 


PREFACE 

The  purpose  of  this  volume  is  to  present  the  principles 
of  the  chemistry  of  food  and  nutrition  with  special  refer- 
ence to  the  food  requirements  of  man  and  the  considerations 
which  should  underlie  our  judgment  of  the  nutritive  values 
of  food.  The  food  is  here  considered  chiefly  in  its  nutritive 
relations.  It  is  hoped  that  the  more  detailed  description 
of  individual  foods  and  the  chemical  and  legal  control  of 
the  food  industry  may  be  treated  in  a  companion  volume 
later. 

The  present  work  is  the  outgrowth  of  several  years' 
experience  in  teaching  the  subject  to  collegiate  and  technical 
students  who  have  represented  a  considerable  diversity  of 
previous  training  and  points  of  view,  and,  while  published 
primarily  to  meet  the  needs  of  the  author's  classes,  it  is 
hoped  that  it  may  also  be  of  service  to  students  and  teachers 
elsewhere  and  to  general  readers  whose  main  interests  may 
lie  in  other  fields,  but  who  appreciate  the  importance  of 
food  and  nutrition  as  factors  in  hygiene  and  preventive 
medicine. 

While  neither  the  size  nor  the  purpose  of  this  book  would 
permit  an  historical  or  technically  critical  treatment,  a 
limited  number  of  historical  investigations  and  controverted 
views  have  been  mentioned  in  order  to  give  an  idea  of  the 
nature  and  validity  of  the  evidence  on  which  our  present 
beliefs  are  based,  and  in  some  cases  to  put  the  reader 
on  his  guard  against  theories  which,  while  now  outgrown, 
are  still  sometimes  encountered. 


266992 


VI  PREFACE 

The  author  desires  to  express  his  indebtedness  to  the 
former  students  and  other  friends  who  have  aided  him  with 
helpful  suggestions,  and  specifically  to  Miss  M.  Helen  Keith 
and  Miss  Mildred  D.  Schlesinger  for  assistance  in  the  revision 
of  manuscript  and  proof. 


CONTENTS 


PAGB 

Introduction i 


CHAPTER   I 
The  Organic  Foodstuffs 4 

CHAPTER  n 
The  General  Composition  of  Foods  and  Action  of  Ferments      41 

CHAPTER  III 

The  Course  of  the  Food  through  the  Digestive  Tract        .      55 

CHAPTER   IV 
The  Fate  of  the  Foodstuffs  in  Metabolism    ....      84 

CHAPTER  V 

The  Fuel  Value  of  Food  and  the  Energy  Requirement  of 

THE  Body 118 

CHAPTER  VI 

Conditions  affecting  the  Total  Food  Requirement       .        .    148 

CHAPTER  VII 

Protein  Metabolism  and  the  Protein  Requirement        .        .176 

vii 


Vm  CONTENTS 

CHAPTER  VIII 

PAGE 

Food  Habits  and  Dietary  Standards 205 

CHAPTER  IX 
Iron  in  Food  and  its  Functions  in  Nutrition         .  231 

CHAPTER  X 

Inorganic  Foodstuffs  and  the  Mineral  Metabolism       .        .    260 

CHAPTER  XI 

Criteria  of  Nutritive  Value  and  Economy  of  Foods     .        .    298 

APPENDIX 

Edible  Organic  Nutrients  and  Fuel  Value  of  F(jods  .  .319 

Ash  Constituents  in  Percentage  of  Edible  Portion  .  .    332 

Ash  Constituents  in  ioo-Calorie  Portions  of  Foods  .  .    338 


/  CHEMISTRY 

OF 

FOOD  AND   NUTRITION 


CHEMISTRY  OF   FOOD  AND 
NUTRITION 

INTRODUCTION 

The  activities  on  which  the  life  of  the  body  depends  in- 
volve a  continuous  expenditure  of  energy  and  a  constant 
breaking  down  of  body  constituents.  The  energy  expended 
leaves  the  body  chiefly  as  heat;  the  material  expenditures 
of  the  body  are  showii  in  the  various  end-products  eliminated 
through  the  lungs,  skin,  kidneys,  and  intestines.  We  may 
consider  all  those  substances  which  supply  the  body  either 
with  matter  needed  for  its  substance  or  with  energy  for  its 
activities  as  collectively  constituting  its  food,  and  any  in- 
dividual compound  which  thus  nourishes  the  body  may  be 
considered  a  nutrient  or  a  foodstuff.  The  energy  expended 
by  the  body  is  derived  from  the  burning  of  organic  materials, 
chiefly  carbohydrates,  fats,  and  proteins.  The  material  ex- 
pended includes  compounds  of  carbon,  hydrogen,  oxygen, 
nitrogen,  sulphur,  phosphorus,  chlorine,  sodium,  potassium, 
calcium,  magnesium,  and  iron.  These  expenditures  are  un- 
avoidable. They  may  be  reduced,  but  can  never  be  stopped ; 
neither  by  resting  the  body  as  completely  as  possible,  nor  by 
stopping  the  intake  of  food. 


2  CHEMISTRY    OF   FOOD   AND   NUTRITION 

The  nutrition  of  the  body  includes  all  those  processes  which 
have  to  do  with  the  upbuilding  and  repairing  of  the  tissues 
and  supplying  them  mth  fuel  for  their  work.  Lusk  defines 
nutrition  as:  The  sum  of  the  processes  concerned  in  the 
growth,  maintenance,  and  repair  of  the  living  body  as  a 
whole,  or  of  its  constituent  organs. 

Most  of  the  nutrient  material  contained  in  food  requires 
more  or  less  change  to  bring  it  into  the  exact  forms  most 
useful  in  nutrition.  These  changes  as  a  rule  take  place  in 
the  digestive  tract  and  together  constitute  the  process  of 
digestion. 

The  changes  which  take  place  in  the  foodstuffs,  after  they 
have  been  absorbed  from  the  digestive  tract,  are  included 
under  the  general  term  "  metabolism."  Although  the 
chemical  changes  and  the  energy  transformations  are  of 
course  inseparable,  it  has  become  customary  to  speak  of  the 
metaboUsm  of  matter  and  the  metabolism  of  energy,  and  to 
regard  the  extent  of  the  metaboUsm  of  any  material  sub- 
stance as  measured  by  the  amount  of  its  end-products  elimi- 
nated, and  the  extent  of  the  energy  metaboUsm  as  measured 
by  the  amount  of  heat,  or  of  heat  and  external  muscular 
work,  which  the  body  gives  off. 

The  metaboUsm  of  matter  and  the  metaboUsm  of  energy 
are  normally  supported  by  the  food ;  but  if  no  food  is  taken, 
they  continue  at  the  expense  of  the  body  substance.  The 
expenditure  of  energy  can  never  cease  in  the  Uving  body 
because  it  includes  the  work  involved  in  carrying  on  the  in- 


INTRODUCTION  3 

ternal  processes  which  are  essential  to  life  itself;  and  the 
expenditure  of  matter  cannot  cease  because  the  energy  for 
this  necessary  work  is  obtained  by  the  breaking  down  of  the 
organic  compounds  of  the  food  or  of  the  body  substance  into 
simpler  compounds,  many  of  which  are  of  no  further  use  to 
the  body  and  must  be  eliminated.  When  the  food  suppUes 
sufficient  energy,  the  body  substance  is  protected ;  when  the 
food  is  insufficient,  body  substance  is  burned  as  fuel,  and  the 
waste  of  the  materials  which  make  up  the  body  tissues  is 
increased.  In  order,  then,  to  consider  intelligently  the  nu- 
tritive requirements  of  the  body  as  regards  the  substances  ^ 
of  which  it  is  composed,  it  is  necessary  first  to  know  "whether 
the  fuel  requirements  (the  requirements  of  the  energy  me- 
tabolism) have  been  fully  met. 

The  plan  of  the  present  work  is  (i)  to  describe  briefly  the 
principal  foodstuffs  and  the  agencies  and  processes  through 
which  they  become  available  for  the  uses  of  the  body; 
(2)  to  follow  their  functions  in  the  tissues  and  their  fate  in 
metaboHsm ;  (3)  to  determine  the  food  requirements  of  the 
body  under  different  conditions ;  (4)  to  ascertain  the  func- 
tions of  the  individual  chemical  elements  in  nutrition  and 
the  quantities  in  which  they  should  be  supplied  by  the  food ; 
(5)  to  consider  the  criteria  by  which  we  should  judge  the 
nutritive  value  and  economy  of  articles  of  food.  This  order 
of  study  has  been  found  advantageous  both  from  the  stand- 
point of  food  chemistry  and  of  application  to  the  practical 
problems  of  human  nutrition. 


CHAPTER  I 

THE  ORGANIC  FOODSTUFFS 

CARBOHYDRATES 

The  carbohydrates  include  the  simple  sugars  and  all 
those  more  complex  substances  (such  as  dextrin,  starch, 
etc.)  which  by  hydrolysis  can  be  resolved  into  simple  sugars. 
%  Of  the  constituents  of  an  ordinary  mixed  diet  the  carbo- 
hydrates are  usually  the  most  abundant  and  the  most  eco- 
nomical. They  are  also  the  first  of  the  three  great  groups  of 
foodstuffs  to  be  formed  by  S3nithesis  from  simple  inorganic 
substances  in  plants. 

The  chlorophyll  cells  of  the  leaves  of  green  plants  utilize 
the  energy  of  the  sun's  rays  to  bring  about  reactions  between 
carbon  dioxide  and  water,  wdth  the  liberation  of  oxygen  and 
the  formation  of  an  organic  compound.  There  is  still  some 
doubt  as  to  the  exact  mechanism  of  the  process,  but  the  vol- 
ume of  oxygen  liberated  is  equal  to  the  volume  of  carbon 
dioxide  which  disappears,  and  whatever  the  intermediate 
products,  there  is  normally  an  early  production  of  carbohy- 
drate. If  the  intermediate  stages  be  omitted,  the  net  result 
may  be  represented  schematically  as  follows :  — 

6  CO2  +  6  H2O  =  CeHisOe  +  6  O2. 
4 


THE    0RGA2^IC   FOODSTUFFS  5 

There  is  much  evidence  that  formaldehyde  is  an  intermediate 
product,  and  according  to  the  recent  work  of  Usher  and 
Priestley,^  hydrogen  peroxide  is  also  produced.  Such  a 
reaction  might  be  represented  by  the  equation :  — 

CO2  +  3  H2O  =  CH2O  +  2  H,02. 

Under  the  influence  of  the  chlorophyll  cell  the  hydrogen 
peroxide  is  rapidly  decomposed  into  water  and  oxygen,  and 
the  formaldehyde  built  up  into  carbohydrate.  Glucose  and 
other  sugars  belonging  to  the  simplest  group  of  carbohy- 
drates are  in  composition  direct  polymers  of  formaldehyde 
and  are  classified  as  hexoses,  pentoses,  etc.,  according  to  the 
number  of  carbon  atoms  in  the  molecule. 

Two  pentoses,  xylose  and  arabinose,  have  been  obtained 
from  both  animal  and  vegetable  sources  and  are  of  consider- 
able biological  interest;  but  by  far  the  most  important  and 
best-known  carbohydrates  are  the  hexoses  and  their  anhy- 
drides. 

The  nine  carbohydrates  of  most  importance  in  human  food 
and  nutrition  may  be  grouped  as  follows :  — ■ 

Monosaccharides  —  simple    sugars,    those   which    cannot 

be    split    by    hydrolysis    into    sugars    of    lower    molecular 

weight ;  — 

Glucose 

Fructose  v 

Galactose 

*  Proc.  Royal  Society  (B),  77,  369  ;  78,  318  (1906). 


6  CHEMISTRY   OF   FOOD    AND    NUTRITION 

Disaccharides  —  sugars  each  of  which  can  be  split  by 
hydrolysis  to  yield  two  molecules  of  monosaccharide :  — 

Sucrose 
Lactose 
Maltose 

Polysaccharides  ^  —  anhydrides  of  unknown  molecular 
weight,  each  molecule  yielding  an  undetermined  number 
of  molecules  of    monosaccharide   when   completely  hydro- 

lyzed :  — 

Starch 

Dextrin 
Glycogen 

Monosaccharides 

The  monosaccharides  are  all  soluble,  crystallizable,  diffus- 
ible substances,  unaffected  by  digestive  enzymes,  and  if  not 
attacked  by  bacteria  in  the  digestive  tract,  they  are  absorbed 
and  enter  the  blood  current  imchanged.  All  of  those  here 
considered  have  the  formula  CeHioOe,  are  susceptible  to  alco- 
hoHc  fermentation,  and  are  utilized  for  the  production  of 
glycogen  in  the  animal  body  and  the  maintenance  of  the 
normal  glucose  content  of  the  blood.  A  few  of  the  leading 
facts  regarding  the  occurrence  in  food  and  the  nutritive 
relations  of  the  individual  monosaccharides  are  given  below. 

Glucose  (d.  glucose,  dextrose,  grape  sugar,  starch  sugar, 

*  Some  writers  use  the  term  "  polysaccharides  "  to  include  all  carbo- 
hydrates other  than  monosaccharides. 


THE    ORGANIC  FOODSTUFFS  ^      7 

diabetic  sugar)  is  widely  distributed  in  nature,  occurring  in 
the  blood  of  all  animals  in  small  quantity  (usually  about 
O.I  per  cent),  and  more  abundantly  in  fruits  and  plant  juices, 
where  it  is  usually  associated  with  levulose  and  sucrose.  It 
is  especially  abundant  in  grapes,  of  which  it  often  constitutes 
20  per  cent  or  more  of  the  weight  of  the  fresh  fruit  and  con- 
siderably more  than  half  of  the  soUd  matter.  Sweet  corn, 
onions,  and  unripe  potatoes  are  among  the  common  vege- 
tables containing  considerable  amounts  of  glucose. 

Glucose  is  also  obtained  from  many  other  carbohydrates 
by  hydrolysis  either  by  acids  or  by  enzymes,  and  thus  be- 
comes the  principal  form  in  which  the  carbohydrate  of  the 
food  enters  into  the  animal  economy.  In  the  healthy  ani- 
mal body  the  glucose  of  the  blood  is  constantly  being  burned 
and  replaced.  In  diabetes  the  body  loses  to  a  greater  or  less 
degree  the  power  to  burn  glucose,  which  then  accumulates 
in  excessive  amount  in  the  blood,  from  which  it  escapes 
through  the  kidneys.  A  temporary  and  usually  unimpor- 
tant loss  of  glucose  in  the  urine  may  occur  as  the  result  of 
feeding  large  quantities  at  a  time.  This  condition  is  known 
as  ahmentary  glycosuria.  Ordinarily  any  surplus  of  glucose 
absorbed  from  the  digestive  tract  is  converted  into  glycogen 
in  the  liver. 

Fructose  {d.  fructose,  fruit  sugar,  levulose)  occurs  with 
more  or  less  glucose  in  plant  juices,  in  fruits,  and  especially 
in  honey,  of  which  it  constitutes  about  one  half  the  solid 
matter.     It   results   in   equal   quantity  with  glucose   from 


8  CHEMISTRY    OF    FOOD    AND    NUTRITION 

the  hydrolysis  of  cane  sugar  and  in  smaller  proportion  from 
some  other  less  common  sugars.  There  also  occurs  in  a  few 
food  plants  {e.g.  in  the  bulb  of  the  Jerusalem  artichoke) 
a  polysaccharide  —  inulin  —  which  on  hydrolysis  yields 
fructose  only;  but  this  appears  not  to  be  attacked  by  the 
ordinary  digestive  enzymes  and  so  probably  does  not  supply 
fructose  to  the  body.  Fructose  may  occur  in  normal  blood, 
but  probably  only  in  insignificant  amounts.  It  serves,  like 
glucose,  for  the  production  of  glycogen ;  and  the  fructose 
which  enters  the  body  either  through  being  eaten  as  such  or 
as  the  result  of  the  digestion  of  cane  sugar  is  mainly  changed 
to  glycogen  on  reaching  the  liver,  so  that  it  does  not  enter 
largely  into  the  blood  of  the  general  circulation.  Recently 
it  has  been  found  that  glucose  and  fructose  are  partially 
convertible,  either  one  into  the  other,  by  proper  treatment 
with  very  dilute  alkalies.  It  is  not  surprising,  therefore, 
that  fructose  should  be  converted  in  the  liver  into  glycogen 
which  on  hydrolysis  yields  glucose. 

Galactose  is  not  found  free  in  nature,  but  results  from  the 
hydrolysis  of  milk  sugar,  either  by  acids  or  by  digestive  en- 
zymes, and  appears  to  have  the  same  power  as  glucose  and 
fructose  to  promote  the  formation  of  glycogen  in  the  animal 
body.  Anhydrides  of  galactose  known  as  galactans  occur 
quite  widely  distributed  in  plant  products.  The  galactans 
of  certain  legumes  studied  by  Schulze  and  Castro  were 
found  to  be  readily  digested,  while  certain  other  galactans 
are  not. 


THE    ORGANIC   FOODSTUFFS  9 

DiSACCHARIDES 

The  three  disaccharides  here  considered  are  hexo-bioses 
of  the  formula  C12H22O11,  and  are  crystallizable  and  diffusible. 
Sucrose  crystallizes  anhydrous;  maltose  and  lactose,  each 
with  one  molecule  of  water,  which  can  be  removed  by  drying 
at  temperatures  of  100°  and  130°  respectively.  They  are 
soluble  in  water  (lactose  much  less  readily  than  sucrose  and 
maltose),  and  much  more  sparingly  soluble  in  alcohol. 
These  disaccharides  are  important  constituents  of  food  and 
are  changed  to  monosaccharides  during  the  process  of 
digestion. 

Sucrose  (saccharose,  cane  sugar)  is  widely  distributed  in 
the  vegetable  kingdom,  being  found  in  considerable  quantity, 
generally  mixed  with  glucose  and  fructose,  in  the  fruits  and 
juices  of  many  plants.  The  commercially  important  sources 
of  sucrose  are  the  sugar  beet,  the  sugar  and  sorghum  canes, 
the  sugar  palm,  and  the  sugar  maple;  but  many  of  the 
common  fruits  and  vegetables  contain  notable  amounts, 
e.g.  sucrose  is  said  to  constitute  at  least  half  the  solid  mat- 
ter of  pineapples  and  of  some  roots  such  as  carrots.  A 
molecule  of  sucrose  yields  on  hydrolysis  one  molecule  each 
of  glucose  and  fructose.  These  sugars  all  rotate  the  plane 
of  vibration  of  polarized  light,  sucrose  and  glucose  to  the 
right  (+),  and  fructose  to  the  left  (-).  The  terms  "  dex- 
trose" and  "levulose,"  synonyms  for  glucose  and  fructose 
respectively,  arose  from  this  behavior  of  the  sugars  in  rotat- 


lO  CHEMISTRY    OF    FOOD    AND    NUTRITION 

ing  the  plane  of  polarized  light  to  the  right  and  left.  Since 
at  ordinary  temperatures  the  fructose  rotates  more  strongly 
to  the  left  than  the  glucose  does  to  the  right,  the  result  of 
the  hydrolysis  is  to  change  the  sign  of  rotation  from  +  to  — . 
For  this  reason  the  hydrolysis  of  cane  sugar  is  often  called 
"inversion,"  and  the  resulting  mixture  of  equal  parts  glucose 
and  fructose  is  known  as  "invert  sugar." 

Sucrose  is  very  easily  hydrolyzed  either  by  acid  or  by  the 
sucrase  ("invertase"  or  "inverting"  enz3mie)  of  yeast  or  of 
intestinal  juice.  So  far  as  known  neither  the  saHva  nor  the 
gastric  juice  contains  any  enzyme  capable  of  hydrolyzing 
cane  sugar,  and  the  slight  amount  of  hydrolysis  which  takes 
place  in  the  stomach  is  beUeved  to  be  due  simply  to  the 
presence  of  hydrochloric  acid.  Under  normal  conditions 
the  sucrose  of  the  food  passes  mainly  into  the  intestine  un- 
changed and  is  there  spUt  by  the  sucrase  of  the  intestinal 
juice,  and  the  resulting  glucose  and  fructose  are  absorbed 
into  the  portal  blood. 

When  large  amounts  of  sucrose  are  fed,  some  absorption 
takes  place  in  the  stomach ;  but  the  unchanged  sucrose  thus 
absorbed  appears  to  be  largely,  if  not  wholly,  lost  through 
the  kidneys,  as  it  is  when  injected  directly  into  the  blood 
current.  Sugar  eaten  in  considerable  quantities  at  a  time 
is  apt  to  undergo  lactic  acid  fermentation  in  the  stomach. 
According  to  Herter,  sucrose  and  glucose  are  more  Hable  to 
such  fermentation  than  lactose.  In  cases  where  fermentation 
does  not  occur  and  the  sucrose  itself  has  no  irritating  effect. 


THE    ORGANIC   FOODSTUFFS  II 

it  may  be  especially  useful  as  a  rapidly  available  foodstuJff. 
It  is  not  known  whether  sucrose  has  any  advantage  over 
maltose  and  lactose  in  this  respect. 

Lactose  (milk  sugar)  occurs  in  the  milk  of  all  mammals, 
constituting  usually  from  4  to  7  per  cent  of  the  fresh  secre- 
tion. At  the  time  of  parturition,  or  if  the  milk  is  not  with- 
drawn from  the  udder,  some  lactose  may  occur  in  the  urine. 
If  in  such  a  case  the  mammary  glands  are  removed,  the  per- 
centage of  glucose  in  the  blood  increases,  and  glucose  (but  no 
lactose)  may  appear  in  the  urine.  These  observations  in- 
dicate that  lactose  is  formed  in  the  mammary  gland  and 
probably  from  the  glucose  brought  by  the  blood  (Abder- 
halden). 

When  hydrolyzed  either  by  heating  with  acids  or  by  the 
lactase  of  the  intestinal  juice,  each  molecule  of  lactose  yields 
one  molecule  of  glucose  and  one  of  galactose.  In  normal 
digestion  probably  none  of  the  lactose  eaten  is  absorbed  as 
such,  for  lactose  injected  into  the  blood  is  eliminated  quickly 
and  almost  completely  through  the  kidneys,  whereas  large 
amounts  of  lactose  can  be  taken  by  the  mouth  without  any 
such  loss. 

Maltose  (malt  sugar)  is  formed  from  starch  by  the  action 
of  diastatic  enzymes  (amylases)  and  is  therefore  an  important 
constituent  of  germinating  cereals,  malt,  and  malt  products. 
It  is  also  formed  as  an  intermediate  product  when  starch 
is  hydrolyzed  by  boiling  with  dilute  mineral  acids,  as  in  the 
manufacture  of  commercial  glucose. 


12  CHEMISTRY   OF   FOOD   AND   NUTRITION 

In  animal  digestion  maltose  is  formed  by  the  action  of 
the  ptyalin  of  the  saliva  or  the  amylopsin  of  the  pancreatic 
juice  upon  starch  or  dextrin.  The  maltose-spUtting  enzyme 
of  the  intestinal  juice  readily  hydrolyzes  maltose  to  glucose. 
Maltose  is  also  readily  and  completely  hydrolyzed  by  boiUng 
with  dilute  mineral  acids. 

While  it  is  probable  that  Httle  if  any  maltose  is  absorbed 
as  such  from  the  digestive  tract  under  ordinary  conditions, 
it  is  possible  that  such  absorption  may  occur  and  that  malt- 
ose as  such  may  play  a  part  in  the  normal  carbohydrate 
metabolism ;  for  when  injected  into  the  blood  it  appears  to 
be  utilized  to  better  advantage  than  either  sucrose  or  lactose, 
and  it  may  be  obtained  from  glycogen  by  the  action  of  dia- 
static  enzymes  in  much  the  same  way  as  from  starch  and 
dextrin  (Abderhalden). 

Polysaccharides 

The  polysaccharides  are  all  imcrystallizable,  non-diffusible, 
and  insoluble  in  alcohol.  Some  dissolve  in  water,  some 
swell  and  become  gelatinous,  some  are  unchanged.  The 
members  of  greatest  importance  in  nutrition  are  starch  and 
glycogen,  the  typical  reserve  carbohydrates  of  plants  and 
animals  respectively. 

Starch,  (CeHioOs)^:,  is  the  form  in  which  most  plants  store 
the  greater  part  of  their  carbohydrates,  and  is  of  great  im- 
portance as  a  constituent  of  many  food  materials  and  as  the 
source  of  dextrin,  maltose,  coromercial  glucose,  and  many 


THE    ORGANIC   FOODSTUFFS  13 

fermentation  products.  Starch  is  found  stored  in  the  seeds, 
roots,  tubers,  bulbs,  and  sometimes  in  the  stems  and  leaves, 
of  plants.  It  constitutes  one  half  to  three  fourths  of  the 
solid  matter  of  the  ordinary  cereal  grains  and  at  least  three 
fourths  of  the  solids  of  mature  potatoes.  Unchanged  starch 
occurs  in  distinct  granules,  and  those  formed  in  different 
plants  vary 'in  size  and  structure,  so  that  in  most  cases  the 
source  of  a  starch  which  has  not  been  altered  by  heat,  re- 
agents, or  ferments  can  be  determined  by  microscopical 
examination.  Starch  granules  are  scarcely  affected  by  cold 
water;  on  warming  they  absorb  water  and  swell.  Finally 
the  starch  passes  into  a  condition  of  colloidal  solution  or 
semisolution,  "starch  paste."  A  more  perfect  solution  is 
readily  obtained  by  the  use  of  water  containing  a  small 
amount  of  caustic  alkali.  The  best-known  reaction  of 
starch  is  the  formation  of  an  intense  blue  compound  with 
iodine  in  the  cold.  The  granular  forms  of  the  starches 
produced  in  different  plants  are  often  characteristic. 

When  treated  with  hydrochloric  acid  (usually  7  to  10  per 
cent)  in  the  cold  or  with  very  moderate  warming,  more  or 
less  hydration  occurs  with  the  production  of  "soluble  starch." 
Starch  on  hydrolysis  gives  first  mixtures  of  dextrin  and 
maltose,  and  finally  glucose  only  as  an  end-product.  The 
most  satisfactory  hydrolysis  of  starch  to  glucose  is  accom- 
plished by  boiling  or  heating  in  a  boiling  water  bath  with 
hydrochloric  acid  of  a  concentration  of  about  2.5  per  cent. 
When  brought  in  contact  with  saliva,  starch  is  hydrolyzed 


14  CHEMISTRY   OF   FOOD   AND   NUTRITION 

by  the  ptyalin  with  the  formation  of  dextrin  and  maltose. 
A  similar  hydrolysis  is  effected  by  amylopsin,  the  starch- 
sphtting  enzyme  of  the  pancreatic  juice.  ! 

DextrinSj  (CeHioOo)^  or  (CeHioOs)^.  •  H2O,  are  formed  from 
starch  by  the  action  of  enzymes,  acids,  or  heat.  Small 
amounts  of  dextrin  are  found  in  normal,  and  larger  amounts 
in  germinating,  cereals.  Malt  diastase  acting  upon  starch 
in  fairly  concentrated  solution  yields  usually  about  one  part 
of  dextrin  to  four  of  maltose.  During  acid  hydrolysis, 
dextrin  is  formed  as  an  intermediate  product  between  soluble 
starch  and  maltose.  Commercial  dextrin,  the  principal 
constituent  of  "British  gum,"  is  obtained  by  heating  starch, 
either  alone  or  with  a  small  amount  of  dilute  acid. 

The  splitting  of  dextrin  has  already  been  mentioned  in 
connection  w^ith  that  of  starch,  both  ptyalin  and  amylopsin 
forming  dextrin  as  an  intermediate  product  and  acting  upon 
it  with  the  production  of  maltose.  Complete  hydrolysis  of 
dextrin  yields  glucose  as  the  sole  product. 

Glycogen,  (CeHioOs)^,  plays  much  the  same  role  in  animals 
which  starch  plays  in  plants,  and  is  sometimes  called  "animal 
starch."  Glycogen  also  takes  the  place  of  starch  as  reserve 
carbohydrate  in  fungi  and  other  forms  of  plant  life  not  pro- 
vided with  the  chlorophyll  apparatus.  It  is  a  white,  amor- 
phous powder,  odorless  and  tasteless,  which  swells  up  and 
apparently  dissolves  in  cold  water  to  a  colloidal  opalescent 
solution  which  is  not  cleared  by  repeated  filtration,  but  loses 
its  opalescence  on  addition  of  a  very  small  amount  of  po- 


THE    ORGANIC   FOODSTUFFS  1 5 

tassium  hydroxide  or  acetic  acid.  Water  solutions  of  gly- 
cogen treated  with  iodine  react  yellow-brown,  red-brown, 
or  deep  red.  Acid  hydrolysis  yields  glucose  only  as  end- 
product. 

Glycogen  occurs  in  the  lower  as  well  as  the  higher  animals, 
and  in  all  parts  of  the  body,  but  is  especially  abundant  in 
the  liver,  where  it  is  found  deposited  in  the  cell  substance 
but  not  in  the  nucleus.  The  amount  of  glycogen  in  the  liver 
depends  to  a  great  extent  upon  the  condition  of  nutrition  of 
the  animal.  In  the  average  of  seven  experiments  by  Schon- 
dorff  in  which  dogs  were  fed  for  the  production  of  as  much 
glycogen  as  possible,  2,^  per  cent  of  that  found  was  in  the 
liver,  44  per  cent  in  the  muscles,  9  per  cent  in  the  bones, 
and  the  remaining  9  per  cent  in  the  other  tissues  and  the 
fluid  of  the  body.  But  the  distribution  of  glycogen  in  the 
body  as  shown  by  these  experiments  was  quite  variable, 
even  among  animals  of  the  same  species  which  had  been  fed 
in  the  same  way;  while  it  is  well  known  that  some  species 
store  glycogen  in  their  muscles  to  a  greater  extent  than  others, 
attempts  even  having  been  made  to  distinguish  between 
horseflesh  and  beef  by  the  difference  in  their  glycogen 
content. 

The  storage  of  glycogen  in  the  body  is  promoted  by  rest 
as  well  as  by  liberal  feeding,  and  stored  glycogen  is  used 
up  rapidly  during  active  muscular  work. 


l6  CHEMISTRY   OF   FOOD   AND   NUTRITION 

FATS 

Fats  are  glycerol  esters  of  fatty  acids,  and  since  glycerol 
is  a  triatomic  alcohol  and  the  fatty  acids  are  monatomic, 
a  normal  glyceride  is  a  triglyceride  and  on  hydrolysis  yields 
three  molecules  of  fatty  acid  and  one  molecule  of  glycerol. 
Thus,  for  example :  — 

C3H5(Cl8H3502)3  +  3  H2O   =    C3H5(OH)3  +  3  C18H36O2. 

Stearin  Glycerol  Stearic  acid 

(glyceryl  tristearate) 

When  the  splitting  of  the  fat  is  brought  about  by  means  of 
an  alkali  instead  of  water,  the  corresponding  products  are 
glycerol  and  three  molecules  of  the  alkali  salt  of  the  fatty 
acid.  Alkali  salts  of  the  fatty  acids  being  commonly  known 
as  soaps,  this  reaction  is  usually  called  saponification  of  the 
fat. 

The  fats  are  therefore  a  definite  group  of  chemical  com- 
pounds, and  the  term  applies  equally  to  the  sohd  and  the 
liquid  members  of  this  group.  As  a  matter  of  convenience, 
however,  the  Uquid  fats  are  often  called  "fatty  oils."  The 
fatty  oils  are  also  sometimes  called  fixed  oils,  since  a  spot 
made  by  dropping  a  fatty  oil  on  paper  cannot  be  removed 
by  drying  (as  can  a  volatile  oil),  nor  by  washing  with  water 
(as  can  glycerin).  All  of  the  fats  are  practically  insoluble 
in  water,  and  all  except  those  of  the  castor  oil  group  are 
sparingly  soluble  in  cold  alcohol,  but  dissolve  readily  in 
petroleum  ether  and  mix  in  all  proportions  with  light  petro- 


THE    ORGANIC   FOODSTUFFS  1 7 

leum  oils.  All  of  the  fats  are  readily  soluble  in  ether,  carbon 
bisulphide,  chloroform,  carbon  tetrachloride,  and  benzene. 
All  natural  fats  contain  small  amounts  of  free  fatty  acid 
and  of  other  substances  aside  from  the  glycerides  of  which 
they  are  principally  composed.  The  actual  glycerides  of 
any  common  natural  fat,  with  the  exception  of  butter,  would, 
if  obtained  absolutely  pure,  be  colorless,  tasteless,  and  odor- 
less. The  colors,  tastes,  and  odors  of  fats  are  therefore 
ordinarily  due  to  substances  present  in  small  amount  which 
might  be  removed  by  refining  processes. 
'  All  of  the  quantitative  differences  among  the  fats  are  to  be 
accounted  for  by  the  kinds  and  the  amounts  of  the  fatty  acids 
which  enter  into  the  composition  of  the  glycerides.  The 
greater  number  of  the  fatty  acids  belong  to  a  few  homologous 
series.  The  series  to  which  stearic  acid  belongs  may  be  rep- 
resented by  the  general  formula  C^H2„02,  and  is  made  up 
of  homologues  of  acetic  acid.  The  principal  members  of 
physiological  importance  are  as  follows:  — 

AaDS  OF  THE  Series  C„H2„02 

Butyric  acid  (C4H8O2)  occurs  as  glyceride  to  the  extent  of 
about  5  to  6  per  cent  in  butter  and  in  very  small  quantities 
in  a  few  others  fats. 

Caproic  acid  (C6H12O2)  is  obtained  from  goat  and  cow 
butter  and  cocoanut  fat. 

Caprylic  acid   (C8H16O2)  is  obtained  from  cocoanut  oil, 
butter,  and  human  fat. 
c 


1 8  CHEMISTRY    OF   FOOD    AND    NUTRITION 

Capric  acid  (C10H20O2)  is  obtained  from  cocoanut  oil, 
butter,  and  the  fat  of  the  spice  bush. 

Laurie  acid  (C12H24O2)  occurs  abundantly  -as  glyceride  in 
the  fat  of  the  seeds  of  the  spice  bush,  and  in  smaller  propor- 
tions in  butter,  cocoanut  fat,  palm  oil,  and  some  other 
vegetable  oils. 

Myristic  acid  (C14H28O2)  is  obtained  from  nutmeg  butter, 
cocoanut  oil,  butter,  lard,  and  many  other  fats,  as  well  as 
from  spermaceti  and  wool  w^ax. 

Palmitic  acid  (C16H32O2)  occurs  abundantly  in  a  great 
variety  of  fats,  both  animal  and  vegetable,  including  many 
fatty  oils,  and  also  in  several  waxes,  including  spermaceti  and 
beeswax. 

Stearic  acid  (CisHagOo)  is  found  in  most  fats,  occurring 
most  abundantly  in  the  solid  fats  and  especially  in  those 
having  high  melting  points. 

Butyric  acid  is  a  mobile  liquid,  mixing  in  all  proportions 
with  water,  alcohol,  and  ether,  boiling  without  decomposition, 
and  readily  volatile  with  steam.  With  increasing  molecular 
weight  the  acids  of  this  series  regularly  show  increasing 
boiling  or  melting  points,  decreasing  solubility,  and  loss  of 
volatility  with  steam.  Stearic  acid  is  a  crystalline  solid, 
insoluble  in  water  and  only  moderately  soluble  in  alcohol 
and  ether. 

Acids  of  the  Series  C,iH2„-o02 

These  are  unsaturated  compounds.  Each  molecule  con- 
tains one  ethylene  linkage  or  double  bond,  and  can  take  up  by 


THE    ORGANIC   FOODSTUFFS  19 

addition  two  atoms  of  halogen  to  form  a  saturated  compound.^ 
These  unsaturated  acids  have,  as  a  rule,  much  lower  melting 
points  than  the  saturated  acids  containing  the  same  number 
of  carbon  atoms.  The  glycerides  show  correspondingly 
lower  melting  points  than  those  of  the  saturated  fatty  acids 
and  are  therefore  found  more  largely  in  the  soft  fats  and  the 
fatty  oils. 

Phycetoleic  acid  (C16H30O2)  is  obtained  from  seal  oil  and 
sperm  oil ;  an  isomeric  acid,  hypogaeic,  occurs  in  peanut  oil. 

Oleic  acid  (C18H34O2)  occurs  as  glyceride  in  nearly  all 
fats  and  fatty  oils  and  is  much  the  most  important  member 
of  the  series.  Many  of  the  typical  oils  of  both  animal  and 
vegetable  origin,  such  as  lard  oil  and  olive  oil,  consist 
mainly  of  olein. 

Erucic  acid  (C22H42O2)  is  obtained  from  rape  seed  and 
mustard  seed  oils,  and  is  not  found  in  animal  fats  except 
when  oils  which  contain  this  acid  have  been  fed  to  the  animal. 

The  gradual  change  in  physical  properties  with  increasing 
molecular  weight  which  is  noticeable  in  the  stearic  acid  series, 
is  not  apparent  in  this  series,  probably  because  the  known 
acids  of  the  series  differ  as  regards  the  position  of  the  double 
bond  and  are  therefore  not  strictly  homologous. 

1  The  relative  number  of  double  bonds  is  measured  analytically  by 
determining  the  percentage  of  iodine  which  the  fat  or  fatty  acid  will 
absorb.  Thus  pure  oleic  acid  (mol.  wt.  282)  absorbs  2  atoms  of  iodine, 
giving  an  "iodine  number"  of  go;  pure  Hnoleic  acid  would  absorb 
4  atoms-of  iodine  to  the  molecule,  giving  an  "iodine  number"  about 
twice  as  great. 


20  shemistry  of  food  and  nutrition 

Other  Unsaturated  Fatty  Acids 

Acids  of  the  series  C„H2;j_402,C„H2„_^02  and  C„H2„_802 
have  been  found  to  occur  as  glycerides  in  some  of  the  fats. 
Linoleic  acid,  C18H32O2,  and  linolenic  acid,  C18H30O2,  are  the 
best  known  of  these  acids.  They  are  found  abundantly  in 
Hnseed  oil  and  in  others  of  the  so-called  "drying  oils,"  which 
on  account  of  the  affinity  for  oxygen  of  their  highly  unsatu- 
rated glycerides  oxidize  to  solids  on  exposure  to  the  air.  Fatty 
acids  having  the  same  number  of  double  bonds  but  not  the 
same  property  of  oxidizing  to  hard,  solid  films  are  found  in 
fatty  oils  of  animal  origin,  especially  those  obtained  from 
marine  animals  and  from  fishes.  Since  the  acids  of  this  series 
have  still  lower  melting  points  than  the  corresponding  acids 
of  the  oleic  series,  and  since  the  physical  properties  of  the 
glycerides  follow  those  of  the  fatty  acids  which  they  contain, 
a  fat  containing  an  acid  isomeric  with  linoleic  or  linolenic  acid 
will  be  more  fluid  at  any  given  temperature  than  one  con- 
taining oleic  acid  in  the  same  proportion.  Hence,  it  is  appar- 
ent that  glycerides  of  the  highly  unsaturated  and  more  fluid 
acids  are  physiologically  adapted  to  the  cold-blooded  animals 
and  it  is  found  that  they  are  especially  abundant  in  fish  fat ; 
the  acids  of  the  series  C„H2„_802  have  been  obtained  as  yet 
only  from  fish  oils. 

Composition  of  Animal  Fat 
Just  as  we  find  the  character  of  the  fat  in  the  cold-blooded 
animals  adapted  to  the  low  temperature  to  which  it  is  exposed, 


THE    ORGANIC   FOODSTUFFS  21 

SO  to  a  less  degree  the  character  of  the  fat  of  warm-blooded 
animals  appears  to  vary  with  its  position  in  the  body  and 
with  the  temperature  to  which  the  body  is  subjected  during 
the  time  that  the  fat  is  in  process  of  formation.  Thus  Hen- 
riques  and  Hansen  conclude  from  experiments  with  pigs  that 
the  thick  layer  of  subcutaneous  fat  on  the  back,  where  it  was 
not  thoroughly  warmed  by  the  blood  and  therefore  had  an 
average  temperature  considerably  below  that  of  the  interior 
of  the  body,  was  richer  in  unsaturated  compounds  (olein, 
etc.)  and  had  a  lower  melting  point  than  the  fat  of  the  body 
as  a  whole;  while  the  fat  from  animals  which  had  been  grown 
in  a  warm  room,  or  which  had  been  heavily  jacketed  so  that 
the  skin  was  not  exposed  to  cold  air,  contained  near  the  skin 
fat  of  more  nearly  the  same  composition  as  in  the  interior  of 
the  body. 

Moulton  and  Trowbridge  have  observed  that  the  fat  in  beef 
animals  becomes  richer  in  olein  and  therefore  softer  with  age, 
with  fatness,  and  with  nearness  to  the  surface  of  the  body. 

Usually  the  nature  of  the  fat  found  in  the  body  is  more  or 
less  characteristic  of  each  species  or  group  of  closely  related 
species.  Herbivora  contain  as  a  rule  harder  fats  than  car- 
nivora,  land  animals  have  harder  fat  than  marine  animals, 
and  all  warm-blooded  animals  have  fats  which  are  decidedly 
harder  than  those  found  in  fishes. 

The  body  fats  of  most  land  animals  consist  chiefly  of  glyc- 
erides  of  oleic,  palmitic,  and  stearic  acids.  The  differences 
in  microscopic  appearance  which  distinguish  the  fats  of 


22 


CHEMISTRY   OF    FOOD   AND    NUTRITION 


different  species  are  due  to  variations,  not  only  in  the  amounts 
of  the  fatty  acids  present,  but  also  in  the  manner  of  their 
combination.  A  compound  of  glyceryl  with  three  fatty  acid 
radicles  of  the  same  kind  is  caUed  a  simple  glyceride;  one  con- 
taining two  or  three  different  fatty  acid  radicles  is  known  as 
a  mixed  gylceride.  In  cases  where  fats  of  nearly  the  same 
composition  show  quite  distinct  crystalline  form,  it  is  probable 
that  this  is  largely  due  to  the  presence  of  different  mixed 
glycerides  in  the  different  fats.  This  has  been  shown  to  be 
the  case  with  regard  to  beef  fat,  whose  microscopic  appearance 
permits  its  detection  when  mixed  with  lard.  The  fats  of 
different  mammals  were  investigated  by  Schulze  and  Reineke, 
whose  results  ^  showed  little  variation  from  an  average  of  car- 
bon, 76.5  per  cent;  hydrogen,  12  per  cent;  oxygen,  11.5  per 
cent,  as  may  be  seen  from  the  following :  — 


Carbon 

Hydrogen 

Oxygen 

Human  fat 

Beef  fat 

Mutton  fat 

Pork  fat 

76.62 
76.50 
76.61 
76.54 

11.94 
11.91 
12.03 
11.94 

11.44 

11-59 
11.36 
11.52 

Benedict  and  Osterberg  ^  found  in  8  samples  of  human  fat 
an  average  of  76.08  per  cent  carbon  and  11.78  per  cent 
hydrogen. 

The  foregoing  statements  refer  to  the  fat  of  the  adipose 

^  Armsby  :  Prbuiples  of  Animal  Nutrition,  p.  61. 
*  American  Journal  of  Physiology,  4,  69. 


THE    ORGANIC   FOODSTUFFS  23 

tissues.  In  the  fat  extracted  from  the  liver,  kidney,  and 
heart,  Hartley  ^  finds  fatty  acids  of  the  series  C„H2„_402, 
QHon-^Os,  and  possibly  CJl2n-s02. 

Butter  fat  differs  from  body  fat  in  containing  fatty  acids 
of  lower  molecular  weight  (particularly  butyric  acid,  which  is 
fairly  characteristic  of  butter),  and  so  shows  a  higher  per- 
centage of  oxygen  and  lower  percentages  of  carbon  and  hydro- 
gen. The  most  abundant  acids  of  butter  fat  arc,  however, 
palmitic,  oleic,  and  myristic,  and  the  ultimate  composition  is 
not  very  greatly  different  from  that  of  body  fats.  A  sample 
of  butter  fat  analyzed  by  Browne^  showed  75.17  per  cent 
carbon,  11.72  per  cent  hydrogen,  and  13. 11  per  cent  oxygen. 

PROTEINS 

The  proteins  are  very  complex  and  usually  amorphous 
compounds  differing  in  composition  and  properties,  but  all  of 
high  molecular  weight  and  unknown  or  incompletely  known 
chemical  structure,  though  now  regarded  as  essentially  an- 
hydrides of  amino  acids. 

The  simplest  of  these  amino  acids  is  amino-acetic  acid, 
commonly  called  glycocoU  or  glycin,  CH2NII2 — COOH. 
Two  molecules  of  glycin  combined  by  elimination  of  one 
molecule  of  water  yield  glycyl-glycin, 

CH2NH2~CO 

I 
CH2NH— COOH, 

^Journal  of  Physiology,  36,  17. 

^Journal  American  Chemical  Society,  1899,  21,  823. 


24  CHEMISTRY   OF   FOOD   AND   NUTRITION 

which  is  the  simplest  of  an  immense  group  of  anhydrides  of 
amino  acids,  all  of  which  are  called  "peptids."  Dipeptids 
contain  two  amino-acid  radicles,  tripeptids  contain  three,  etc. 
Fischer,  by  uniting  7  to  i8  amino-acid  radicles,  has  produced 
complex  synthetic  polypeptids  which  in  some  of  their  proper- 
ties resemble  the  peptones.  All  of  the  typical  proteins  contain 
carbon,  hydrogen,  nitrogen,  sulphur,  and  oxygen  ;  some  also 
contain  phosphorus  and  iron.  The  average  ultimate  com- 
position of  the  better-known  proteins  of  the  body  and  of 
the  food  is  approximately  as  follows:  carbon,  53  per  cent; 
hydrogen,  7  per  cent;  nitrogen,  16  per  cent;  sulphur,  i  per 
cent ;  oxygen,  23  per  cent. 

Proteins  differ  in  their  solubility  in  water,  salt  solutions, 
and  alcohol ;  but  are  all  insoluble  in  ether,  chloroform,  carbon 
tetrachloride,  carbon  bisulphide,  benzene,  and  petroleum 
ether. 

Since  the  proteins  are  conspicuously  nitrogen  compounds, 
it  is  important  to  realize  that  other  nitrogen  compounds  also 
occur  in  the  body  and  in  the  food.  Among  these  are  the 
alkaloids,  the  nitrogenous  fats  and  essential  oils,  the  so-called 
nitrogenous  extractives,  and,  among  inorganic  nitrogen  com- 
pounds, ammonium  salts  and  nitrates.  With  the  exception 
of  certain  of  the  "extractives,"  the  amounts  of  these  non- 
protein nitrogen  compounds  in  foods  or  in  the  body  tissues  is 
usually  quite  small.  The  proteins  and  their  immediate  de- 
rivatives constitute  therefore  nearly  all  of  the  nitrogenous 
material  involved  in  nutrition;  and  since  the  proteins  are 


THE    ORGANIC   FOODSTUFFS  25 

somewhat  similar  in  nitrogen  content,  it  has  become  customary 
in  food  analysis  and  nutrition  work  to  take  the  total  nitrogen 
as  a  measure  of  the  protein,  so  that  statements  regarding 
percentages  of  proteins  ordinarily  mean  the  percentage  of 
nitrogen  multiplied  by  6.25,  this  factor  being  based  on  the 
assumption  that  proteins  contain  approximately  16  per  cent 
of  nitrogen. 

A  few  years  ago  an  attempt  was  made  in  this  country  to 
use  the  term  "proteids"  for  definite  substances  of  the  group 
which  we  are  considering,  and  to  reserve  the  term  "  protein  " 
for  the  result  obtained  by  multiplying  figures  for  nitrogen 
by  6.25  or  other  conventional  factor.  This,  however,  was 
thought  by  some  to  be  a  cause  of  confusion,  inasmuch  as 
the  German  word  "Proteid"  designates  only  a  portion  of  the 
compounds  which  in  English  were  called  "proteids."  For  this 
reason  Halliburton  and  Hopkins,  in  behalf  of  the  EngHsh 
physiological  chemists,  have  submitted  a  revision  of  the 
terminology  of  these  bodies  in  which  the  term  "  proteid  "  is 
dropped,  and  now  a  joint  committee  of  the  American  Physio- 
logical Society  and  the  American  Society  of  Biological  Chem- 
ists have  concurred  in  this  recommendation  while  proposing 
a  terminology  which  differs  in  detail  from  any  previously 
suggested  and  which,  as  indorsed  by  the  two  societies,  is  as 
follows :  — 


26  CHEMISTRY    OF    FOOD    AND    NUTRITION 


Joint  Recommendations  of  the  Committees  on  Protein 
Nomenclature 

Since  a  chemical  basis  for  the  nomenclature  of  the  proteins 
is  at  present  not  possible,  it  seemed  important  to  recommend  few 
changes  in  the  names  and  definitions  of  generally  accepted  groups, 
even  though,  in  many  cases,  these  are  not  wholly  satisfactory. 
The  recommendations  are  as  follows :  — 

First.  —  The  word  ''  proteid  "  should  be  abandoned. 

Second.  —  The  word  ''  protein  "  should  designate  that  group  of 
substances,  which  consist,  so  far  as  at  present  is  known,  essen- 
tially of  combinations  of  a-amino  acids  and  their  derivatives,  e.g. 
a-amino  acetic  acid  or  glycocoll ;  a-amino  propionic  acid  or  alanin ; 
phcnyl-a-amino  propionic  acid  or  phenylalanin ;  guanidin-a-amino 
valerianic  acid  or  arginin,  etc. ;  and  are  therefore  essentially 
polypeptids. 

Third.  —  That  the  following  terms  be  used  to  designate  the 
various  groups  of  proteins :  — 

I.  Simple  Proteins.  —  Protein  substances  which  yield  only 
a-amino  acids  or  their  derivatives  on  hydrolysis. 

Although  no  means  are  at  present  available  whereby  the  chemi- 
cal individuality  of  any  protein  can  be  established,  a  number  of 
simple  proteins  have  been  isolated  from  animal  and  vegetable 
tissues  which  have  been  so  well  characterized  by  constancy  of 
ultimate  composition  and  uniformity  of  physical  properties  that 
they  may  be  treated  as  chemical  individuals  until  further 
knowledge  makes  it  possible  to  characterize  them  more  defi- 
nitely. 

The  various  groups  of  simple  proteins  may  be  designated  as 
follows :  — 

(a)  Albumins.  —  Simple  proteins  soluble  in  pure  water  and 
coagulable  by  heat. 

(b)  Globidins.  —  Simple  proteins  insoluble  in  pure  water  but 


THE    ORGANIC   FOODSTUFFS  27 

soluble  in  neutral  solutions  of  salts  of  strong  bases  with  strong 
acids/ 

(c)  Glutelins.  —  Simple  proteins  insoluble  in  all  neutral  solvents 
but  readily  soluble  in  very  dilute  acids  and  alkalies.^ 

(d)  Alcohol-soluble  Proteins.  —  Simple  proteins  soluble  in  rela- 
tively strong  alcohol  (70-80  per  cent),  but  insoluble  in  water, 
absolute  alcohol,  and  other  neutral  solvents.^ 

(e)  Albuminoids.  —  Simple  proteins  which  possess  essentially 
the  same  chemical  structure  as  the  other  proteins,  but  are  charac- 
terized by  great  insolubility  in  all  neutral  solvents.^ 

(/)  Histones.  —  Soluble  in  water  and  insoluble  in  very  dilute 
ammonia,  and,  in  the  absence  of  ammonium  salts,  insoluble  even 
in  an  excess  of  ammonia ;  yield  precipitates  with  solutions  of 
other  proteins  and  a  coagulum  on  heating  which  is  easily 
soluble  in  very  dilute  acids.  On  hydrolysis  they  yield  a  large 
number  of  amino  acids,  among  which  the  basic  ones  pre- 
dominate. 

(g)  Protamins.  —  Simpler  polypeptids  than  the  proteins  in- 
cluded in  the  preceding  groups.  They  are  soluble  in  water,  un- 
coagulable  by  heat,  have  the  property  of  precipitating  aqueous 
solutions  of  other  proteins,  possess  strong  basic  properties,  and 
form  stable  salts  with  strong  mineral  acids.     They  yield  com- 

1  The  precipitation  limits  with  ammonium  sulphate  should  not  be 
made  a  basis  for  distinguishing  the  albumins  from  the  globulins. 

2  Such  substances  occur  in  abundance  in  the  seeds  of  cereals  and  doubt- 
less represent  a  well-defined  natural  group  of  simple  proteins. 

2  The  subclasses  defined  (a,  h,  c,  d)  are  exemplified  by  proteins 
obtained  from  both  plants  and  animals.  The  use  of  appropriate  pre- 
fixes will  suffice  to  indicate  the  origin  of  the  compounds,  e.g.  ovoglobulin, 
myoalbumin,  etc. 

^  These  form  the  principal  organic  constituents  of  the  skeletal  struc- 
ture of  animals  and  also  their  external  covering  and  its  appendages. 
This  definition  does  not  provide  for  gelatin,  which  is,  however,  an  arti- 
ficial derivative  of  collagen. 


28  CHEMISTRY    OF    FOOD   AXD    NUTRITION 

paratively  few  amino  acids,  among  which  the  basic  amino  acids 
greatly  predominate. 

II.  Conjugated  Proteins.  —  Substances  which  contain  the  pro- 
tein molecule  united  to  some  other  molecule  or  molecules  other- 
wise than  as  a  salt. 

(a)  Nucleoproteins.  —  Compounds  of  one  or  more  protein  mole- 
cules with  nucleic  acid. 

{b)  Glycoproteins.  —  Compounds  of  the  protein  molecule  with  a 
substance  or  substances  containing  a  carbohydrate  group  other 
than  a  nucleic  acid. 

(c)  Phosphoproteins.  —  Compounds  of  the  protein  molecule 
with  some,  as  yet  undefined,  phosphorus-containing  substance 
other  than  a  nucleic  acid  or  lecithin.^ 

{d)  HcfHoglobifis.  —  Compounds  of  the  protein  molecule  with 
hematin  or  some  similar  substance, 

(e)  Lecitho proteins.  —  Compounds  of  the  protein  molecule  with 
lecithins  (lecithans,  phosphatids). 

III.  Derived  Proteins. 

I.  Primary  Protein  Derivatives.  —  Derivatives  of  the  protein 
molecule  apparently  formed  through  hydrolytic  changes  which  in- 
volve only  shght  alterations  of  the  protein  molecule. 

{a)  Proteans.  —  Insoluble  products  which  apparently  result 
from  the  incipient  action  of  water,  very  dilute  acids,  or  enzymes. 

{b)  Metaproteins.  —  Products  of  the  further  action  of  acids 
and  alkalies  whereby  the  molecule  is  so  far  altered  as  to  form 
products  soluble  in  very  weak  acids  and  alkahes,  but  insoluble  in 
neutral  fluids. 

This  group  will  thus  include  the  familiar  "acid  proteins"  and 
"alkaU  proteins,"  not  the  salts  of  proteins  with  acids. 

(c)  Coagulated  Proteins.  —  Insoluble  products  which  result  from 

^  The  accvimulated  chemical  evidence  distinctly  points  to  the  pro- 
priety of  classifying  the  phosphoproteins  as  conjugated  compounds,  i.e. 
they  are  possibly  esters  of  some  phosphoric  acid  or  acids  and  protein. 


THE    ORGANIC   FOODSTUFFS  29 

(i)  the  action  of  heat  on  their  solutions,  or  (2)  the  action  of  alco- 
hols on  the  protein. 

2.  Secondary  Protein  Derivatives}  —  Products  of  the  further 
hydrolytic  cleavage  of  the  protein  molecule. 

{a)  Proteoses.  —  Soluble  in  water,  uncoagulated  by  heat,  and 
precipitated  by  saturating  their  solutions  with  ammonium  sul- 
phate or  zinc  sulphate.^ 

(6)  Peptones.  —  Soluble  in  water,  uncoagulated  by  heat,  but  not 
precipitated  by  saturating  their  solutions  with  ammonium  sul- 
phate.^ 

(c)  Peptids.  —  Definitely  characterized  combinations  of  two  or 
more  amino  acids,  the  carboxyl  group  of  one  being  united  with  the 
amino  group  of  the  other,  with  the  elimination  of  a  molecule  of 
water.* 

Notes  on  Some  of  the  More  Important  Proteins 

Albumins  and  globulins  are  very  often  associated,  as, 
for  example,  in  blood  serum  and  in  the  cell  substance.  The 
typical  albumins  are  richer  in  sulphur  than  the  typical  glob- 
ulins. As  a  rule  the  albumins  are  the  more  abundant  in 
animal  fluids  (blood,  etc.),  while  the  globulins  predominate 

^  The  term  secondary  hydrolytic  derivatives  is  used  because  the  for- 
mation of  the  primary  derivatives  usually  precedes  the  formation  of 
these  secondary  derivatives. 

2  As  thus  defined,  this  term  does  not  strictly  cover  all  the  protein  de- 
rivatives commonly  called  proteoses,  e.g.  heterproteose  and  dysproteose. 

^  In  this  group  the  kyrins  may  be  included.  For  the  present  we  be- 
lieve that  it  will  be  helpful  to  retain  this  term  as  defined,  reserving  the 
expression  "  peptid  "  for  the  simpler  compounds  of  definite  structure, 
such  as  dipeptids,  etc. 

*  The  peptones  are  undoubtedly  peptids  or  mixtures  of  peptids,  the 
latter  term  being  at  present  used  to  designate  those  of  definite  structure. 


30  CHEMISTRY    OF    FOOD    AND    NUTRITION 

over  albumins  in  animal  tissues  and  in  plants.  There  ap- 
pears to  be  no  sharp  di\ading  line  between  the  albimiins  and 
the  globuUns.  While  the  globulins  are  insoluble  in  pure  water, 
a  water  extract  of  animal  tissue  (muscle,  for  example)  will 
contain,  in  addition  to  albumin,  a  considerable  amount  of 
globulin  carried  into  solution  hy  the  salts  present  in  the 
tissue,  and  if  the  salts  are  removed  as  completely  as  possible 
by  dialysis,  some  of  the  globuhn  still  remains  in  solution; 
separations  based  upon  saturation  with  neutral  salts  are 
also  apt  to  be  unsatisfactory  (Howell). 

Alcohol-soluble  proteins  and  gliitelins  are  chiefly  important 
as  constituents  of  the  cereal  grains.  The  best-known  ex- 
amples of  the  respective  groups  are  gliadin  and  glutenin  of 
wheat  flour.  These  proteins  resemble  each  other  in  ulti- 
mate composition,  but  differ  not  only  in  solubihties,  but  also 
in  their  cleavage  products.  They  are  much  the  most  im- 
portant of  the  proteins  of  the  wheat  kernel,  the  gliadin 
making  up  about  50  per  cent  and  the  glutenin  about  40  per 
cent  of  the  total  protein  present.  These,  of  course,  are 
approximate  average  figures.  In  individual  samples  of 
wheat  considerable  variation  in  the  proportions  of  both  gliadin 
and  glutenin  may  be  found.  The  gliadin  and  glutenin  to- 
gether constitute  the  gluten  of  wheat  flour.  The  elasticity 
and  strength  of  the  gluten  and  therefore  the  baking  qualities 
of  the  flour  are  influenced  by  the  proportions  of  gliadin  and 
glutenin  present,  about  twice  as  much  gliadin  as  glutenin 
being  usually  considered  desirable  in  bread  flour. 


THE    ORGANIC   FOODSTUFFS  3 1 

Albuminoids  have  often  been  classified  in  a  group  apart 
from  the  "true  proteins"  not  so  much  on  account  of  their 
known  chemical  or  physical  properties  as  because  it  was 
found  that  gelatin,  which  was  considered  typical  of  the  group, 
did  not  alone  satisfactorily  support  the  protein  metaboUsm 
of  the  body  (see  Chapters  VII  and  XI).  This  distinction 
has  lost  much  of  its  force  since  proteins  of  other  groups  fed 
singly  have  also  in  some  cases  been  found  unable  to  support 
protein  metabolism,  and  the  albuminoids  are  now  reassigned 
to  a  place  among  the  true  proteins. 

Nucleoproteins  are  the  characteristic  proteins  of  cell  nuclei 
and  are  therefore  especially  abundant  in  the  highly  nu- 
cleated cells  of  the  glandular  organs,  such  as  the  thymus, 
the  pancreas,  and  the  liver.  They  are  compounds  of  simple 
proteins  with  nucleic  acid  or  nuclein.  On  digestion  with 
pepsin-hydrochloric  acid  nucleoprotein  splits,  with  the  for- 
mation, first,  of  a  simple  protein  and  a  nuclein.  The  latter 
on  further  decomposition  yields  a  simple  protein  and  nucleic 
acid.  Nucleic  acid  is  therefore  the  characteristic  constit- 
uent, and  a  number  of  different  forms,  all  rich  in  phos- 
phorus, have  been  described  under  such  names  as  thymo- 
nucleic  acid,  tritico-nucleic  acid,  guanylic  acid,  etc.  On 
hydrolytic  decomposition  they  yield  some  of  the  purin  bases 
(xanthin,  adenin,  guanin,  etc.),  some  pyrimidin  derivatives 
(uracil,  thymin,  cytosin),  a  carbohydrate  group,  and  phos- 
phoric ^cid. 


32 


CHEMISTRY    OF    FOOD    AND    NUTRITION 


The  cleavage  products  of  nucleoproteins  may  therefore  be 
represented  as  follows :  — 


Proteins 


Proteins 


Nucleoproteins 

Nucleins 
Nucleic  acids 


Carbohydrates  Phosphoric  acid  Bases 


Purins 

Adenin 

Guanin 

Hypoxanthin 

Xanthin 
Pyrimidins 

Thymin 

Cytosin 

Uracil 


Phosphoproteins  occur  especially  in  milk  and  eggs,  the 
foods  most  obviously  intended  to  provide  the  material  for 
growth  and  development.  The  phosphorus,  wMe  probably 
present  in  the  form  of  a  more  or  less  modified  phosphoric 
acid  radicle,  appears  to  be  more  closely  bound  in  these  than 
in  the  nucleoproteins.  Casein  of  milk  and  vitellin  of  egg- 
yolk  (ovo-vitellin)  are  the  most  prominent  members  of  the 
group.  These  are  sometimes  classed  with  simple  proteins 
under  the  name  nucleoalbumins.  Phosphoprotein  prepa- 
rations show  on  analysis  small  amounts  of  iron,  which  has 
usually  been  neglected  as  an  impurity,  but  which  is  not  im- 
probably an  essential  constituent. 

Hemoglobins  consisting  of  combinations  of  simple  proteins 


THE    ORGANIC   FOODSTUFFS  33 

with  coloring  matter  serve  as  carriers  of  oxygen  from  the  air 
to  the  tissues.  On  boiling  or  heating  with  acids  or  alkalies 
they  split  up  into  their  constituent  parts:  for  example, 
ordinary  hemoglobin  yields  about  4  per  cent  of  hematin, 
C32H32]N4Fe04,  and  a  residue  of  globin  which  was  formerly  con- 
sidered a  globulin  but  is  now  assigned  to  the  hi  stone  group. 

Proteoses  and  peptones  are  products  derived  from  other 
proteins  by  digestion  or  by  simple  hydrolysis.  They  are 
soluble  in  water  and  not  coagulated  by  boiling  their  aqueous 
solutions.  No  sharp  line  can  be  drawn  either  between  prote- 
oses and  peptones,  or  between  peptones  and  the  simpler  nitro- 
gen compounds  which  result  from  prolonged  digestion.  As 
the  terms  are  generally  used,  peptones  may  be  considered  as 
the  products  of  digestion  or  hydrolysis  which  are  still  pro- 
teins as  judged  by  certain  color  reactions  and  are  precipi- 
tated by  strong  alcohol,  but  not  by  saturation  of  their  solu- 
tions with  zinc  or  ammonium  sulphate,  as  is  the  case  with 
proteoses.  Proteoses  (albumoses)  are  intermediate  products 
between  meta-protein  and  peptones.  In  addition  to  the 
protein  reactions  shown  by  peptones,  the  proteoses  are  pre- 
cipitated from  aqueous  solutions  at  ordinary  temperatures 
by  adding  acetic  acid  and  potassium  ferrocyanide,  or  by 
saturating  the  solution  with  zinc  or  ammonium  sulphate. 

The  term  "  peptone  "  was  formerly  applied  to  all  digestion 
products  not  coagulated  by  boiling,  and  is  still  popularly 
used  in  the  same  sense,  the  best  commercial  "peptones" 
consisting  largely  of  proteoses. 


34  CHEMISTRY   OF   FOOD  AND   NUTRITION 

In  the  main  the  composition  of  the  peptones  agrees  fairly 
well  with  the  assumption  that  they  are  essentially  hydrolytic 
products.  The  changes  in  composition  are,  however,  not 
entirely  such  as  would  result  from  simple  hydrations  alone, 
both  Chittenden  and  Kruger  having  found  that  the  change 
from  original  protein  to  peptone  resulted  in  a  loss  of  sulphur 
entirely  out  of  proportion  to  the  diminution  in  the  nitrogen 
content.  This  probably  indicates  that  sulphur  compounds 
simpler  or  less  easily  precipated  than  the  peptones  are  split 
off  comparatively  early  in  the  hydrolysis  of  proteins. 

It  has  been  said  that  the  proteins  are  now  regarded  as 
essentially  anhydrides  of  amino  acids  (the  principal  amino 
acids  of  proteins  are  listed  below).  Synthetic  anhydrides 
of  amino  acids  have  been  prepared  and  are  called  "peptids" 
with  a  prefix  to  indicate  the  number  of  amino-acid  radicles 
in  the  molecule.  Regarding  the  relation  of  peptones  to  these 
synthetic  products  of  known  structure  Abderhalden  {Physio- 
logical Chemistry,  translated  by  Hall,  p.  184)  says :  "  We  must 
admit  that  many  analogies  exist  between  the  synthetic  poly- 
peptids  and  the  peptones.  We  can  make  no  sharp  distinction 
in  this  direction.  We  must  not  lose  sight  of  the  fact  that  we 
are  comparing  a  sharply  defined  chemical  compound  with  a 
mixture.  The  name  '  peptone '  does  not  indicate  any  definite 
compound ;  in  fact,  may  not  even  represent  distinctly  analo- 
gous cleavage  products  of  protein.  It  is  much  better  to 
assume  that  the  peptones  represent  all  stages  of  decomposi- 
tion between  that  of  albumoses  and  the  amino  acids." 


THE    ORGANIC   FOODSTUrFS 


35 


Composition  and  Constitution  of  Proteins 

The  ultimate  composition  of  some  typical  proteins  is  shown 
in  the  following  table :  — 


Composition  of  Some  Typical  Proteins  according  to  Osborne 


Carbon 

PER 
CENT 

Hydro- 
gen 

PER 

CENr 

Nitro- 
gen 

PER  CENT 

Oxygen 

PER  CENT 

Sul- 
phur 

PER 
CENT 

Iron 

PER 
CENT 

Phos- 
phorus 

PER 
CENT 

Egg-albumin     .     . 

52.7s 

7.10 

15-51 

23.024 

I.616 

Lact-albumin 

. 

52.19 

7.18 

15-77 

23-13 

1.73 

Leucosin  .     . 

53-02 

6.84 

16.80 

22.06 

1.28 

Serum-globulin 

52.71 

7.01 

15-85 

23-32 

I. II 

Myosin    .     . 

52.82 

7.11 

16.67 

22.03 

1.27 

Edestin    .     . 

51.50 

7.02 

18.69 

21.91 

0.88 

Legumin  .     . 

51.72 

6.95 

18.04 

22.905 

0.385 

Casein       .     . 

53-13 

7.06 

15-78 

22.37 

0.80 

— 

0.86 

Ovovitellin   . 

51.56 

7.12 

16.23 

23.242 

1.028 

— 

0.82 

Gliadin     .     . 

52.72 

6.86 

17.66 

21.733 

1.027 

Zein     .     .     . 

. 

55.23 

7.26 

16.13 

20.78 

0.60 

Oxyhemoglobin 

54.64 

7.09 

17.38 

20.165 

0.39 

0.335 

— 

From  the  results  of  ultimate  analysis  an  approximate 
indication  of  the  minimum  molecular  weight  may  often  be 
obtained  by  a  very  simple  calculation.  Thus,  oxyhemo- 
globin contains  only  0.335  per  cent  of  iron,  and  since  there 
must  be  at  least  one  iron  atom  in  the  molecule,  it  is  obvious 
from  a  simple  proportion  making  use  of  the  atomic  weight 
of  iron :  — 

o-335*56::ioo::r 


36  CHEMISTRY    OF    FOOD    AND    NUTRITION 

that  the  molecular  weight  of  hemoglobin  must  be  in  the 
neighborhood  of  16,800  or  a  multiple  of  this. 

To  take  an  example  from  the  simple  proteins,  zein  con- 
tains 0.60  per  cent  of  sulphur,  of  which  one  third  is  much 
more  readily  split  off  than  the  other  two  thirds,  from  which 
it  appears  that  the  molecule  contains  three,  or  a  multiple  of 
three,  sulphur  atoms.     Then  by  the  proportion 

0.60:  {2,2  X  3)  '-'^ooix, 

it  is  found  that  about  16,000  or  a  multiple  thereof  is  the 
probable  molecular  weight  of  zein. 

Our  knowledge  of  the  structure  of  the  protein  molecule 
is  derived  mainly  from  studies  of  the  products  obtained  by 
hydrolytic  cleavage.  Investigations  in  this  direction  are 
being  pursued  very  actively,  and  no  comprehensive  sum- 
mary of  the  results  as  a  whole  can  be  given  in  concise  form 
at  present.  Some  idea  of  the  complexity  of  the  proteins  and 
of  the  great  differences  which  must  exist  in  their  inner  struc- 
ture, may,  however,  be  obtained  from  an  enumeration  of  the 
amino  acids  most  commonly  resulting  from  hydrolysis  of 
proteins  and  from  a  comparison  of  the  yields  obtained  in 
a  few  typical  cases. 

The  more  prominent  amino  acids  are :  — 

Monamino  A  cids : 

Monobasic: 

Glycin  =  amino-acetic  acid,  CH^CNHs)  •  COOH. 
Alanin  =  a-amino-propionic  acid,  CH3CH(NH2)  •  COOH. 


THE    ORGANIC   FOODSTUFFS  37 

Serin  =  a-amino-  )8-hydroxy-propionic  acid, 

CHaCOH)  •  CH(NH2)  •  COOH. 

Valin  =  a-amino-iso valeric  acid, 

(CH3)2CH  .  CH(NH2)  •  COOH. 

Leucin  =  a-amino-caproic  acid  (a-amino-isobutyl-aceticacid), 

(CH3)2CH  .  CH2  •  CH(NH2)  •  COOH. 

Phenylalanin  =  phenyl-a-amino-propionic  acid, 

CeHsCHa  •  CH(NH2)  •  COOH. 

Tyrosin  =  oxyphenyl-a-amino  propionic  acid, 

CeHiCOH)  •  CH2  •  CH(NH2)  •  COOH. 

Dibasic : 

Aspartic  acid  =  amino-succinic  acid, 

COOH  •  CH2  •  CH(NH2)  •  COOH. 

Glutamic   (glutaminic)   acid  =  amino-glutaric  acid, 

COOH  •  CH2  •  CH2  •  CH(NH2)  •  COOH. 

Diamino  Acids : 

Ornithin  =  a,  8,    diamino-valeric  acid, 

CH2(NH2)  •  CH2  •  CH2  •  CH(NH2)  •  COOH. 

Lysin  =  a,   e,   diamino-w-caproic  acid, 

CH2(NH2)  •  CH2  •  CH2  •  CH2  •  CH(NH2)  •  COOH. 

Arginin  =  8-guanidino-a-amino-valeric  acid, 

NH 
(H2N)C-  NH  •  CH2  •  CHo  •  CH2  •  CH(NH2)  •  COOH. 


38  CHEMISTRY    OF   FOOD    AND    NUTRITION 

Heterocyclic  Amino  Acids : 

Histidin  =  a-amino  -y8  imidazol  propionic  acid, 


HC    =    C  •  CH2  •  CH(NH2)  •  COOH. 
HN         N 
CH 


Tryptophan  =  indol-amino-propionic  acid, 

"^    — C  •  CH2  •  CH  •  (NH2)  •  COOH. 

II 
CH 

\/\    / 
NH 


Prolin  =  Pyrrolidin-carboxylic  acid, 


H2C  —  CH2 

I  I 

H2C         CH  •  COOH 
\  / 
NH 


Thio-amino  Acid: 


Cystin  =  dicystein  =  union  of  two  molecules  of  amino-thio- 
lactic  acid, 

S— CH2— CH(NH2)  •  COOH 
I 
S— CH2— CHCNHo)  •  COOH. 

The  percentages  of  amino  acids  thus  far  found  in  the 
products  of  hydrolysis  are  given  below  for  a  few  proteins, 
while  the  corresponding  data  for  several  others  will  be  found 
in  Chapter  XI. 


;&,- 


-^  THE    ORGANIC   FOODSTUFFS  ^ 


39 


Casein  1 

HORDEIN  2 

Globini 

Gelatin  » 

Glycin  .     .     . 
Alanin  .     .     . 
Valin    .     .     . 
Leucin  .     .     . 
Prolin  .     .     . 
Phenylalanin . 
Glutamic  acid 
Aspartic  acid  . 
Cystin  .     .     . 
Serin     .     .     . 
Tyrosin     .     . 
Tryptophan  , 
Oxyprolin .     . 
Lysin    .     .     . 
Arginin      .     . 
Histidin     .     . 
Ammonia  .     . 

o 

0.9 

1.0 

10.5 

3-1 

3-2 

II. 0 

1.2 
.06 
•23 
4-5 
1-5 
•25 
5-8o 
4.84 
2-59 
1-95 

0 

0.43 
0.13 
5.67 

13.73 
5-03 

36.3s 

present 
present 

1.67 
present 

0 

2.16 
1.28 
4.87 

0 
4.2    . 

29.0 

2.3 
4.2 

1-7 

4.4 

•3 
.6 

1.5 
present 
1.0 
4-3 
5.4 
1 1.0 

16.5 

.8 

1.0 

2.1 

5-2 

•4 
•9 
.6 

•4 
0 
0 

3-0 
2.81 
7.61 
0.41 
0.4 

Summation    . 

52.62 

71-32 

69.9 

42.1 

These  figures,  in  addition  to  illustrating  the  complexity 
of  the  protein  molecules,  show  wide  differences  among  the 
proteins  as  regards  the  amounts  of  certain  amino  acids  which 
they  yield.  These  differences  in  cleavage  products  represent 
divergencies  of  structure  which  in  all  probability  should  be 
recognized  in  comparing  the  nutritive  values  of  different 
articles  of  food.  To  what  extent  the  animal  body  can  con- 
vert one  amino  acid  into  another  and  to  what  extent  it  is 

*  Abderhalden  and  associates.  2  Osborne  and  associates. 

2  Fischer  and  associates. 


40  CHEMISTRY    OF   FOOD   AND   NUTRITION 

directly  dependent  upon  the  food  for  the  particular  amino 
acids  needed  for  the  construction  of  its  proteins  has  not  yet 
been  determined  in  detail,  but  some  discussion  of  this  ques- 
tion will  be  found  in  Chapter  XI. 

REFERENCES 

Abderhalden.  Textbook  of  Physiological  Chemistry,  Lectures  2  to  13 
(1908). 

Armstrong.     The  Simple  Carbohydrates  and  the  Glucosides  (1910). 

Cohen.     Organic  Chemistry  (1907). 

Fischer.  Untersuchungen  ueber  Aminosauren,  Polypeptide  und  Pro- 
teine  (1906). 

Hammarsten,  Textbook  of  Physiological  Chemistry,  6th  American  edi- 
tion (1911). 

Hartley.  On  the  Nature  of  the  Fat  contained  in  the  Liver,  Kidney  and 
Heart,  Journal  of  Physiology,  38,  353-374  (1909). 

Hawk.    Practical  Physiological  Chemistry,  2d  edition  (1909). 

HoLLEMAN.     Textbook  of  Organic  Chemistry,  3d  English  edition  (1910). 

Leathes.  Die  Synthese  der  Fette  im  Tierkorper.  Ergehnisse  der  Phy- 
siologic, 8,  356-370  (1909). 

Lewkowitsch.     Oils,  Fats,  and  Waxes,  3d  edition  (1904). 

LiPPMANN.     Chemie  der  Zuckerarten,  3d  edition  (1904). 

Mann.     Chemistry  of  the  Proteids  (1906). 

Osborne.     The  Vegetable  Proteins  (1909). 

Die  Pflanzenproteine.   Ergebnisse  der  Physiologic,  10,  47-215  (1910), 

Plimmer.     Chemical  Constitution  of  the  Proteins,  I  and  II  (1908), 

ScHRYVER.     The  General  Character  of  the  Proteins  (1909). 

ToLLEXS.   Handbuch  der  Kohlenhydrate,  Band  I  (1888).   Band  II  (1895). 

Ulzer  and  Klimont.  Allgemeine  und  Physiologische  Chemie  der  Fette 
(1906). 


CHAPTER  II 

THE  GENERAL  COMPOSITION  OF  FOODS  AND  THE 
ACTION  OF  FERMENTS 

Since  the  important  articles  of  food  contain  in  most  cases 
more  than  one  kind  of  foodstuff,  it  is  not  feasible  to  classify 
them  in  the  same  manner  as  the  individual  nutrients,  and 
for  convenience  of  reference  the  examples  given  in  this 
chapter  may  be  grouped  as  in  the  standard  tables  ^  in  the 
order:  meats,  fish,  eggs,  dairy  products,  grain  products 
and  breadstuffs,  sugars  and  starches,  vegetables,  fruits  and 
nuts. 

The  edible  matter  of  food  is  commonly  assumed  to  consist 
of  water,  proteins,  fats,  carbohydrates,  and  ash.  When  an 
article  of  food  also  contains  inedible  matter  or  refuse,  this 
may  be  stated  separately  and  the  composition  of  the  edible 
portion  then  given,  or  the  percentages  of  refuse  and  of  edible 
nutrients  in  the  original  matter  may  be  given  so  as  to  show 
directly  the  percentage  of  each  edible  nutrient  obtained  in 
the  material  as  purchased.  For  example,  loo  lb.  of  beef 
contains  i6  lb.  of  bone  and  84  lb.  of  moist  flesh  of  which 

*  The  Chemical  Composition  of  American  Food  Materials,  by  W.  O. 
Atwater  and  A.  P.  Bryant,  Bull.  28  (revised),  Office  of  Expt.  Stations, 
U.  S.  Dept.  Agriculture  ;  and  Konig,  Chemie  der  menschliche  Nahrungs- 
und  Genuss-mittel. 

41 


42 


CHEMISTRY    OF    FOOD   AND    NUTRITION 


15.4  lb.  are  protein,  15  lb.  fat,  53  lb.  water,  and  0.6  lb. 
ash.  The  composition  may  be  stated  in  either  of  the  follow- 
ing forms :  — 


Composition  of  Beef 


Refuse 

PER  CENT 

Water 

PER   CENT 

Protein 
PER  cent 

Fat 
per  cent 

Ash 

PER  CENT 

.     16.0 

53.0 

15-4 

15.0 

0.6 

Composition  of  Beef 

Refuse 

Edible  Portion 

per  cent 

Water 
per  cent 

Protein 
per  cent 

Fat 
per  cent 

Ash 
per  cent 

16.0 

62.9 

18.3 

17.9 

0.7 

In  order  to  avoid  confusion  and  possible  errors  in  taking 
data  from  tables  of  composition  it  is  important  to  note  in 
which  form  the  percentages  are  stated.  Data  given  in  either 
form  are  of  course  readily  convertible  into  the  other.  Thus 
in  the  above  example  since  the  beef  contains  16  per  cent  of 
refuse  and  84  per  cent  of  moist  edible  matter,  the  percentage 
of  protein  or  fat  in  the  material  as  purchased  divided  by 
0.84  gives  the  percentage  in  the  edible  portion ;  and  the  per- 
centage in  the  edible  portion  multipUed  by  0.84  gives  the 
percentage  in  the  material  as  purchased. 

The  average  proximate  composition  of  the  edible  portion  of 
some  t3^ical  food  materials  is  shown  in  the  following  table :  — 


THE  GENERAL  COMPOSITION  OF  FOODS 

Composition  of  Edible  Portion  of  Typical  Foods  ^ 


43 


Food  Materials 

Water 

PER  CENT 

Protein 
PER  cent 

Fat 

PER  CENT 

Carbohy- 
drate 

PER   CENT 

Ash 

PER   CENT 

Beef,  free  from  visible  fat 

73-8 

22.1 

2.9 

1.2 

Beef,  round  steak,  lean  ^  . 

70.0 

21.0 

7-9 

I.I 

Ham,  smoked,  lean    .     . 

53-5 

20.2 

20.8 

s-s 

Bacon,  smoked  .     .     . 

20.2 

9.9 

64.8 

5.1 

Codfish,  fresh     . 

82.6 

15.8 

0.4 

1.2 

Salmon      .     .     . 

64.6 

21.2 

12.8 

1.4 

Eggs     .... 

73-7 

14.8 

10.5 

1.0 

Milk     .... 

87.0 

3-3 

4.0 

5-0 

0.7 

Butter       .     .     . 

II.O 

I.O 

85.0 

3-0 

Oatmeal    .     .     . 

7-3 

16.1 

7-2 

67.5     , 

1.9 

Rice     .... 

12.3 

8.0 

0.3 

79.0 

0.4 

Wheat  flour  .     . 

11.9 

13-3 

1-5 

72.7 

0.6 

Bread,  white      . 

35-3 

9.2 

1-3 

53-1 

I.I 

Asparagus     .     . 

94.0 

1.8 

0.2 

3-3 

0.7 

Beans,  dried 

12.6 

22.5 

1.8 

59-6 

3-5 

Beans,  string 

89.2 

2.3 

0.3 

7-4 

0.8 

Beets    .     .     . 

87.5 

1.6 

0.1 

9-7 

I.I 

Cabbage   .     . 

91-5 

1.6 

0.3 

5.6 

1.0 

Carrots     .     . 

88.2 

I.I 

0.4 

9-3 

1.0 

Celery       .     . 

94.5 

I.I 

O.I 

3-3 

1.0 

Corn,  green  . 

75-4 

3-1 

I.I 

19.7 

0.7 

Lettuce     .     . 

94-7 

1.2 

0-3 

2.9 

0.9 

Potatoes  .     . 

78.3 

2.2 

0.1 

18.4 

1.0 

Spinach     .     . 

92.3 

2.1 

0.3 

3.2 

2.1 

Tomatoes 

94-3 

0.9 

0.4 

3-9 

0.5 

Turnips    .     . 

89.6 

1-3 

0.2 

8.1 

0.8 

Apples      .     . 

84.6 

0.4 

0.5 

14.2 

0.3 

Bananas   .     . 

75-3 

1-3 

0.6 

22.0 

0.8 

Currants,  dried 

17.2 

2.4 

1-7 

74.2 

4.5 

Oranges    .     . 

86.9 

0.8 

0.2 

11.6 

0.5 

Peaches     .     . 

89.4 

0.7 

0.1 

9.4 

0.4 

Pineapple 

89-3 

0.4 

0.3 

9-7 

0.3 

Plums  .     .     . 

78.4 

1.0 

20.1 

0.5 

Prunes,  dried 

22.3 

2.1 

73-3 

2.3 

Raisins      .     . 

14.6 

2.6 

3-3 

76.1 

3-4 

Strawberries . 

90.4 

1.0 

0.6 

7-4 

0.6 

Almonds  .     . 

4.8 

21.0 

54-9 

17-3 

2.0 

Chestnuts      . 

45 -o 

6.2 

5-4 

42.1 

1-3 

Peanuts    .     . 

9.2 

25.8 

38.6 

24.4 

2:0 

Olive  oil    .     . 

• 

lOO.O 

A  more  comprehensive  table  will  be  found  in  the  Appendix. 
*  Based  on  Bull.  28,  loc.  cit.,  to  which   the  reader  is  referred   foi 


44     •  CHEMISTRY    OF   FOOD   AND    NUTRITION 

With  few  exceptions  the  nutrients  thus  composing  the 
ordinary  articles  of  food  are  not  of  a  nature  to  be  utilized 
advantageously  by  the  body  tissues  in  the  exact  form  in 
which  they  are  eaten,  but  must  usually  undergo  more  or 
less  extensive  alteration  in  the  digestive  tract.  In  so  far 
as  these  digestive  changes  are  chemical  they  are  brought 
about  mainly  by  the  action  of  soluble  ferments,  or  enzymes. 

ENZYMES  AND   THEIR   ACTIONS 

It  may  be  said  that  all  fermentations  are  brought  about 
either  directly  or  indirectly  by  the  activities  of  animal  or 
vegetable  organisms  or  cells.  When  an  organism  or  a  cell 
acts  directly  and  the  chemical  changes  occur  only  in  its 
presence,  the  fermentation  is  said  to  be  due  to  an  organized 
ferment.  When  the  action  is  not  brought  about  directly 
by  the  cell  itself,  but  by  means  of  a  substance  secreted  by 
the  cell  but  acting  apart  from  it,  this  substance  is  called 
a  soluble  or  unorganized  ferment,  or  (more  commonly  now) 
an  enzyme. 

The  distinction  between  fermentations  due  to  organized 
ferments  and  those  caused  by  enzymes  was  for  a  time  con- 
sidered quite  sharp,  but  was  considerably  shaken  when 
Buchner,  in  1896- 189  7,  showed  that  alcoholic  fermentation, 

analyses  of  other  articles  of  food  and  for  the  composition  of  food  ma- 
terials as  purchased,  including  refuse. 

1  Since  much  of  the  fat  of  these  meats  is  ordinarily  trimmed  off,  the 
composition  of  medium  lean  cuts  is  given  here  as  representing  what  is 
usually  eaten. 


THE  GENERAL  COMPOSITION  OF  FOODS      45 

which  had  been  considered  typical  of  the  fermentations  due 
to  organisms,  might  be  induced  by  an  expressed  juice  of 
the  yeast  entirely  free  from  living  cells.  The  yeast  enzyme 
which  thus  produces  alcoholic  fermentations  is  called  zymase. 
Further  experiments  have  shown  that  many  other  fermenta- 
tions formerly  supposed  to  be  due  to  the  direct  action  of 
organisms  can  be  produced  in  sterile  media  by  enzymes 
obtained  from  the  organisms  with  which  the  fermentation 
is  ordinarily  associated.  The  present  tendency  is  therefore 
to  ascribe  fermentations  in  general  to  enzymes,  although  not 
all  fermentations  have  yet  been  shown  to  take  place  in  the 
absence  of  living  matter.  It  has  been  suggested  that  en- 
zymes be  designated  as  intracellular  or  extracellular  according 
as  they  normally  operate  within  or  without  the  cell  by 
which  they  are  formed,  notwithstanding  the  fact  that  it  is 
possible  by  artificial  means  to  cause  intracellular  enzymes 
to  act  independently  of  cells. 

Enzymes  as  Catalyzers.  —  Under  favorable  conditions  the 
amount  of  material  which  may  be  changed  by  a  given  amount 
of  enzyme  is  so  great  as  to  indicate  that  the  enzyme  acts  as 
a  catalyzer,  and  is  not  used  up  in  the  reaction  which  it  brings 
about.  Thus,  one  part  of  Hammarsten's  rennin  coagulated 
400,000  to  800,000  parts  of  milk  and  must  therefore  have 
produced  a  distinct  chemical  change  in  at  least  10,000  to 
20,000  times  its  weight  of  protein ;  while  Petit  has  described 
the  preparation  of  a  pepsin  powder  which  in  seven  hours 
dissolved  500,000  times  its  weight  of  fibrin. 


46  CHEMISTRY    OF    FOOD   AND    NUTRITION 

A  catalyzer  is  usually  considered  to  alter  the  velocity 
of  a  reaction  but  not  to  initiate  it.  Thus  hydrogen  peroxide 
decomposes  spontaneously  into  water  and  oxygen.  In  a 
pure  aqueous  solution  this  change  goes  on  slowly,  but  it  is 
very  greatly  accelerated  by  the  presence  of  a  minute  amount 
of  colloidal  platinum.  Blood  and  tissue  extracts  contain 
enzymes  which  accelerate  the  decomposition  of  hydrogen 
peroxide  apparently  in  much  the  same  way  as  does  platinum, 
and  the  present  tendency  is  to  regard  the  enzymes  generally 
as  acting  quite  like  the  inorganic  catalyzers  in  altering  by 
their  presence  the  velocity  of  certain  reactions.  Some  of 
the  best-known  enzyme  actions,  however,  fit  into  this  view 
only  theoretically;  for  example,  proteins  in  water  at  ordi- 
nary temperature  do  not  appear  to  split  up  spontaneously 
into  the  products  formed  by  pepsin,  and  if  the  pepsin  be  con- 
sidered as  simply  accelerating  a  reaction  already  taking 
place,  it  must  also  be  considered  that  at  ordinary  tempera- 
tures the  reaction  is  infinitely  slow  so  that  it  cannnot  be 
demonstrated.  At  sufiiciently  high  temperatures,  however, 
protein  undergoes  in  water  alone  a  change  similar  to  that  of 
peptic  digestion. 

Specificity  of  Enzymes.  —  As  compared  with  most  inor- 
ganic catalyzers  the  enzymes  are  strikingly  specific  in  their 
action.  Thus  the  hydrolysis  of  sucrose  may  be  accelerated 
by  hydrochloric  acid  or  b}^  the  enzyme  sucrase;  but  while 
the  acid  similarly  accelerates  the  hydrolysis  of  the  greatest 
variety  of  other  substances,  the  enzyme  acts  upon  sucrose 


THE  GENERAL  COMPOSITION  OF  FOODS       47 

alone  and  appears  to  be  inactive  towards  all  other  substances, 
even  though  they  may  be  readily  susceptible  to  hydrolysis. 

Fischer  suggests  that  this  specificity  of  the  different 
enzymes  may  be  related  to  the  geometrical  structure  or 
special  configuration  of  the  substance  acted  upon,  each 
enzyme  being  adapted  to  act  only  upon  a  molecule  of  a  certain 
definite  structure,  to  which  it  is  fitted  as  a  key  to  its  lock. 

On  the  basis  of  the  properties  which  have  been  outlined, 
Oppenheimer  suggests  and  Howell  adopts  the  following 
descriptive  definition:  An  enzyme  is  a  substance  produced 
by  living  cells,  which  acts  by  catalysis.  The  enzyme  itself 
remains  unchanged  in  this  process,  and  it  acts  specifically  — 
that  is,  each  enzyme  exerts  its  activity  only  upon  substances 
whose  molecules  have  a  definite  structural  and  stereochemical 
arrangement.  The  enzymes  of  the  body  are  organic  sub- 
stances of  a  colloidal  structure  whose  chemical  composition 
is  unknown. 

Classification.  —  Enzymes  are  classified  according  to  their 
effects,  some  of  the  better-known  groups  being  as  follows :  — 

1.  The  hydrolytic  enzymes. 

a.  Proteolytic  or  protein-splitting  enzymes. 
h.  Lipolytic  or  fat-splitting  enzymes. 

c.  Amylolytic  or  starch-splitting  enzymes. 

d.  Sugar-splitting  enzymes. 

2.  The  coagulating  enzymes,  such  as  thrombin  or  throm- 
base  (the  fibrin  ferment),  and  rennin,  which  causes  the  clotting 
of  sweet  milk. 


48  CHEMISTRY    OF   FOOD   AND   NUTRITION 

3.  The  oxidizing  enzymes,  or  "oxidases"  (which,  if  the 
oxidation  be  accompanied  by  a  spHtting  off  of  amino  groups, 
may  be  called  " deamidizing "  or  " deaminizing "  enzymes). 

4.  The  reducing  enzymes  or  "reductases." 

5.  Those  which  produce  carbon  dioxide  without  using 
free  oxygen  —  such  as  the  zymase  of  yeast. 

6.  Enzymes  causing  a  breaking  dow^n  of  a  larger  into  a 
smaller  molecule  of  the  same  composition,  as  in  the  produc- 
tion of  lactic  acid  from  glucose. 

Terminology.  —  In  the  terminology  of  the  enzymes  no 
uniform  system  has  yet  been  adopted.  Most  writers  follow 
in  the  main  the  suggestion  of  Duclaux  that  each  enz)mie  be 
designated  by  the  name  of  the  substance  upon  which  it  acts 
with  the  suffix  ase  {e.g.  protease,  lipase,  amylase,  maltase); 
but  a  few"  of  the  enzymes  which  have  been  longest  know^n 
continue  to  be  called  by  their  original  names  —  ptyalin, 
pepsin,  trypsin,  etc.  Lippmann,  referring  particularly  to  the 
enzymes  of  the  carbohydrates,  proposes  that  the  name  of  the 
enzyme  be  compounded  from  that  of  the  substance  acted  upon 
and  that  of  the  substance  produced  {e.g.  amylo-maltase, 
malto-glucase) ;  but  such  a  terminology  would  become  un- 
wieldy if  an  attempt  were  made  to  apply  it  to  enzymes  in 
general. 

Digestive  Enzymes.  —  The  action  of  digestive  enzymes 
upon  the  foodstuffs  consists  in  splitting  the  latter  into  sub- 
stances of  lower  molecular  weight  which  are  more  readily 
soluble  and  diffusible  and  better  fitted  for  absorption.     The 


THE  GENERAL  COMPOSITION  OF  FOODS       49 

principal  digestive  enzymes  attacking  the  three  groups  of 
organic  foodstuffs  are:  (i)  ptyalin  of  the  saliva,  amylopsin 
of  the  pancreatic  juice,  and  the  sucrase,  maltase,  and  lactase 
of  the  intestinal  juice,  all  of  which  act  upon  carbohydrates ; 
(2)  the  lipases  of  the  gastric  and  pancreatic  juices,  which 
act  upon  fats ;  (3)  pepsin,  trypsin,  and  erepsin  of  the  gas- 
tric, pancreatic,  and  intestinal  juices  respectively,  all  of 
which  act  upon  proteins. 

The  enzymes  are  soluble  in  water,  moderately  soluble  in 
glycerin,  insoluble  in  strong  alcohol.  Heated  to  boiling  in 
water  solution,  any  enzyme  permanently  loses  its  activity, 
but  preparations  which  have  been  carefully  desiccated  are 
only  weakened  and  not  destroyed  by  heating  in  a  dry  state 
to  100°. 

Some  enzymes  are  very  sensitive  to  the  reaction  of  the 
medium  in  which  they  act,  while  others  are  much  less  so; 
thus  pepsin  requires  a  certain  acidity,  while  trypsin  works 
best  in  an  alkaline  medium  but  is  also  moderately  active 
in  neutral  or  even  faintly  acid  solutions. 

Since  all  enzymes  are  soluble  in  water  and  exert  their 
activity  in  solution,  the  speed  of  an  enzyme  action  is  much 
greater  when  the  substance  attacked  is  also  in  solution  than 
when  it  is  in  an  insoluble  state.  In  the  latter  case,  however, 
the  action  may  be  greatly  accelerated  by  finely  dividing  the 
insoluble  substance  so  as  to  expose  a  large  surface  to  the 
action  of  the  solution  containing  the  enzyme.  Since  fats 
are  practically  insoluble  in  water,  it  follows  that  a  sufficient 


50  CHEMISTRY    OF   FOOD   AND   NUTRITION 

contact  of  an  enzyme  with  the  fat  to  bring  about  any  rapid 
hydrolysis  of  the  latter  can  occur  only  when  the  fat  is  emul- 
siJ&ed  so  as  to  expose  a  very  large  surface.  For  this  reason 
the  fat-spHtting  enzyme  of  the  gastric  juice  can  cause  an 
appreciable  digestion  of  fat  in  the  stomach  provided  the 
fat  is  eaten  in  an  emulsified  form  (e.g.  milk,  cream,  or 
egg-yolk),  but  not  otherwise.  In  the  small  intestine,  the 
conditions  are  extremely  favorable  for  the  emulsification 
as  well  as  for  the  splitting  of  the  fat,  so  that  here  even 
relatively  large  masses  of  fat  may  be  broken  up  and  di- 
gested. 

Zymogens  aiid  Activating  Substances. — Within  the  cell  pro- 
ducing it  an  enzyme  often  exists  in  an  inactive  form  known 
as  the  zymogen,  or  antecedent  of  the  active  enzyme.  The 
zymogen  may  be  stored  in  the  cell  in  the  form  of  granules 
which  are  converted  into  active  enzyme  at  the  time  of 
secretion,  or  the  secretion  may  be  poured  out  with  the 
zymogen  not  yet  completely  changed  to  active  enzyme,  or 
sometimes  in  a  form  which  requires  the  action  of  some 
other  substance  in  order  to  render  it  active.  In  this  case 
the  latter  substance  is  said  to  "activate"  the  enzyme. 
The  pancreas  furnishes  an  example  of  a  zymogen  in  its 
external  and  of  an  activating  substance  in  its  internal 
secretion. 

If  the  pancreatic  juice  be  collected  directly  from  the  duct 
and  in  such  a  way  as  to  avoid  all  contact  T\'ith  intestinal 
contents  or  intestinal  mucous  membrane,  it  is  without  effect 


THE  GENERAL  COMPOSITION  OF  FOODS       5 1 

on  coagulated  protein,  because  the  juice  as  secreted  by  the 
pancreas  contains  no  trypsin,  but  a  precursor  of  trypsin 
called  trypsinogen.  This  trypsinogen  is  converted  into 
trypsin  by  the  action  of  intestinal  juice  or  by  contact  with 
the  intestinal  mucous  membrane.  The  substance  derived 
from  the  cells  of  the  intestinal  wall  which  thus  activates 
the  proteolytic  power  of  the  pancreatic  juice  is  known  as 
enterokinase,  and  appears  to  be  an  enzyme,  since  its 
activity  is  stopped  by  too  much  acid  or  alkali,  or  by  heat- 
ing to  67°. 

The  pancreas,  in  addition  to  its  external  secretion,  which 
it  pours  out  into  the  intestine  through  the  pancreatic  duct 
as  pancreatic  juice,  also  produces  an  internal  secretion  which 
does  not  collect  in  any  distinct  duct,  but,  is  carried  away  by 
the  blood  which  circulates  through  the  gland.  This  in- 
ternal secretion  of  the  pancreas  contains  a  substance  (more 
stable  to  heat  than  enterokinase  and  probably  not  an  enzyme) 
which  activates  the  glucose-splitting  enzyme  of  the  muscles 
and  which  appears  to  be  essential  to  the  normal  metabolism 
of  carbohydrates  in  the  body. 

Reversibility  of  Enzyme  Action. —  The  activity  of  an  enzyme 
may  be  stopped,  even  when  all  other  conditions  are  favorable, 
by  the  accumulation  of  the  product  of  its  action;  and  in  cer- 
tain circumstances  the  action  of  the  enzyme  may  be  reversed 
so  as  to  accelerate  a  change  in  the  opposite  direction  to  that 
in  which  it  ordinarily  acts.  Thus  Croft  Hill  showed  it  to  be 
possible  to  reverse  the  ordinary  action  of  maltase  so  as  to 


52 


CHEAOSTRY    OF    FOOD    AND    NUTRITION 


make  it  bring  about  a  conversion  of  mono-  into  di-sac- 
charide,  Pottevin  synthesized  triolein  by  means  of  the  pancreas 
ferment,  and  Taylor  and  others  have  demonstrated  a  partial 
reversion  of  the  tryptic  digestion  of  proteins. 

Summary  of  Occurrence  and  Action  of  Enzymes  of  Digestion 
and  Nutrition.  —  The  following  tabular  summary  of  the  oc- 
currence and  action  of  some  of  the  better-known  enzymes  of 
digestion  and  metabolism  is  essentially  as  given  by  Howell  in 
his  Textbook  of  Physiology :  — 


Enzyme 

Where  chiefly  found 

Action 

Ptyalin  (salivary 

Salivary  secretions 

Converts  starch  to 

amylase) 

maltose 

Amylopsin  (pan- 

Pancreatic  juice 

Converts  starch  to 

creatiq  amylase) 

maltose 

Liver  diastase 

Liver 

Converts  glycogen 
to  glucose 

Muscle  diastase 

Muscles 

Converts  glycogen 

Act  on  Car- 
bohydrates 

Invertase 
(Sucrase) 

Litestinal  juice 

to  glucose 
Converts  sucrose  to 
glucose  and  fruc- 
tose 

Maltase 

Intestinal  juice 

Converts  maltose 
to  glucose 

Lactase 

Intestinal  juice 

Converts  lactose  to 
glucose  and  ga- 
lactose 

Glycolytic 

Muscles,  etc. 

Split    and    oxidize 

enzymes 

glucose 

Lipases 

Gastric  and  pancre- 

Split fats  to  fatty 

Act  on  Fats 

atic     secretions, 

acids    and    glyc- 

blood, and  tissues 

erin 

THE    GENERAL   COMPOSITION    OE   FOODS 


53 


Pepsin 

Gastric  juice. 

Splits  proteins  to 
proteoses  and 
peptones 

Trypsin 

Pancreatic  juice 

Splits  proteins  to 
proteoses,  pep- 
tones,    polypep- 

:t  on 

tids   and   amino 

Proteins 

acids 

Erepsin 

Intestinal  juice 

Splits  peptones  to 
amino  acids  and 
ammonia 

Autolytic 

Tissues  generally 

Split     proteins    to 

enzymes 

simpler  com- 
pounds 

Guanase 

Thymus,  adrenals 

Changes  guanin  to 

pancreas 

xanthin 

Adenase 

Spleen,     pancreas. 

Changes  adenin  to 

ct  on 
Purins 

liver 

hypoxanthin 

Oxidases 

Lungs,  liver,  mus- 

Cause oxidation  as 

cles,  etc. 

of     hypoxanthin 

to  xanthin  and  of 

xanthin    to   uric 

acid 

Since  in  the  preceding  pages  the  digestive  enzymes  have 
been  chiefly  cited  to  illustrate  the  properties  of  enzymes  in 
general,  these  being  the  best  understood  and  their  functions 
recognized  as  predominating  in  the  digestive  changes,  it  should 
also  be  stated  in  conclusion  that  the  processes  of  metabolism 
are  probably  equally  dependent  upon  similar  enzymes  con- 
tained in  the  cells,  and  that  some  of  the  transformations 
which  take  place  in  the  body  are  most  readily  explained  on 
the  ground  of  the  reversibility  of  enzyme  action. 


54  CHEMISTRY    OF   FOOD    AND    NUTRITION 

REFERENCES 

Atwater.     Principles   of   Nutrition    and   Nutritive   Value   of   Foods. 

Farmer's  Bull.  142,  U.  S.  Dept.  Agriculture. 
Atwater  and  Bryant.    The  Chemical  Composition  of  American  Food 

Materials.     Bull.  28  (Revised),  Ofl5ce  of  Experiment  Stations,  U.  S. 

Dept.  Agriculture. 
AYLiss.    The  Nature  of  Enzyme  Action  (1908). 
Bredig.     Die    Elemente    der    chemischen     Kinetik,    mit    besonderer 

Beriicksichtigung  der  Katalyse  und  der  Ferment-wirkung.     Ergeh- 

nisse  der  Physiologie,  i,  134-212. 
Cohen.     Organic  Chemistry  (1907),  Chapter  IX. 
Green.     Soluble  Ferments  and  Fermentation  (1904). 
Hutchison.    Food  and  Dietetics. 

KoNiG.     Chemie  der  menschlichen  Nahrungs-  und  Genussmittel. 
Leach.     Food  Inspection  and  Analysis,  2d  ed.  (1909).' 
Oppenheimer.     Ferments  and  their  Actions  (1901). 
Vernon.     Intracellular  Enzymes  (1908). 
Wiley.     Foods  and  their  Adulteration  (1907). 


# 


CHAPTER  III 

THE   COURSE   OF  THE   FOOD   THROUGH   THE 
DIGESTIVE   TRACT 

The  eating  of  food  induces  a  flow  of  saliva  from  great 
numbers  of  minute  glands  in  the  lining  membrane  of  the 
mouth  and  from  the  three  pairs  of  large  salivary  glands.  That 
these  latter  glands  receive  their  stimulus  through  the  nervous 
system  is  shown  by  the  fact  that  actual  contact  of  any  part 
of  the  body  with  the  food  is  not  necessary,  since  secretion  may 
be  started  by  the  sight  or  odor  or  even  the  thought  of  food, 
and  further  that  mechanical  or  electrical  stimulation  of  the 
proper  nerves  will  cause  a  rapid  flow  of  saliva  when  there  is  no 
suggestion  of  food,  and  even  in  the  case  of  an  animal  com- 
pletely under  the  influence  of  ether  or  chloroform.  Mixed 
human  saliva  has  usually  a  faintly  alkaline  reaction  and 
always  contains  ptyalin  (salivary  amylase),  although  its 
amylolytic  power  appears  to  vary  considerably  with  individ- 
uals and  with  the  same  individual  at  different  times  of  the 
day.  As  the  chewing  of  food  mixes  it  with  saliva,  the  diges- 
tion of  starch  and  dextrin  under  the  influence  of  the  ptyalin 
begins  at  once.  The  mode  of  attachment  of  the  jaw  permits 
a  variety  of  movements  in  chewing,  but  as  mastication  is  an 
entirely  voluntary  act,  the  thoroughness  with  which  the  food 
becomes  mixed  with  saliva  is  subject  to  wide  variations. 

55 


56  CHEMISTRY    OF   FOOD    AND   NUTRITION 

Usually  the  food  stays  too  short  a  time  in  the  mouth  for  the 
starch  to  be  acted  upon  there  to  any  great  extent,  and  until 
recently  it  was  supposed  that  salivary  digestion  must  cease 
almost  as  soon  as  the  food  reaches  the  stomach,  since  the 
activity  of  ptyalin  is  quickly  checked  by  even  small  amounts 
of  free  hydrochloric  acid.  It  was  supposed  that  the  food  mass 
must  soon  be  mixed  with  the  gastric  juice  under  the  influence 
of  the  "churning"  of  the  stomach  contents  by  the  muscular 
contraction  of  the  stomach  walls,  which  was  so  interestingly 
described  by  Dr.  Beaumont  about  eighty  years  ago  as  the 
result  of  his  observations  upon  Alexis  St.  Martin,  the  French- 
Canadian  trapper  who  had  received  a  gunshot  wound  in  the 
stomach  which  on  healing  was  found  to  be  closed  only  by  a 
valve  which  had  developed  over  it.  Dr.  Beaumont  succeeded 
in  retaining  St.  Martin  in  his  employ  for  a  number  of  years, 
and  thus  enjoyed  the  unique  opportunity  of  frequently  ob- 
serving the  course  of  gastric  digestion  by  looking  directly 
into  an  otherwise  normal  human  stomach.  From  the  nature 
of  the  case  Dr.  Beaumont's  observations  were  made  entirely 
at  one  point  in  the  stomach.  Here  he  found  during  digestion 
a  vigorous  muscular  churning  and  mixing  of  the  food  mass 
with  the  gastric  juice,  and  for  a  long  time  this  was  supposed 
to  represent  the  state  of  the  entire  stomach  contents.  This 
view  has  now  been  abandoned  as  the  result  of  a  number  of 
recent  investigations,  among  which  those  of  Cannon  and  of 
Griitzner  are  of  especial  interest. 

When  a  small  amount  of  an  inert  metallic  compound  such  as 


THE    COURSE    OF    THE    FOOD  57 

bismuth  subnitrate  is  mixed  with  the  food,  it  becomes  possible 
to  photograph  the  food-mass  within  the  body  by  means  of 
the  Roentgen  rays.  By  the  use  of  this  method  Cannon  has 
carried  out  an  extended  series  of  observations  upon  the  move- 
ments of  the  stomach  and  intestines  during  digestion/  upon 
the  results  of  which  the  statements  concerning  the  mechanism 
of  digestion  in  this  chapter  are  chiefly  based. 

Cannon's  observations,  confirmed  by  those  of  other  in- 
vestigators,  show  that  the  vigorous  muscular  movements 


POSITION    OF 
TRANSVERSE    BAND 


MIDDLE  REGION 

Fig.  I.  —  Diagram  to  show  the  diflferent  parts  of  the  stomach. 

described  by  Beaumont,  and  which  generally  begin  20  to  30 
minutes  after  the  beginning  of  a  meal,  occur  only  in  the  middle 
and  posterior,  or  pyloric,  portion  of  the  stomach;  while  the 
anterior  portion,  or  fundus,  which  serves  as  a  reservoir  for  the 
greater  portion  of  the  food,  is  not  actively  concerned  in  these 

^American  Journal  of  Physiology,  i,  359;  6,251;   12,  387.     These 
papers  are  fully  abstracted  in  Fischer's  Physiology  of  Alimentation. 


58 


CHEMISTRY    OF    FOOD   AND    NUTRITION 


movements  and  does  not  rapidly  mix  its  contents  with  the 
gastric  juice. 

That  there  is  no  general  circulation  and  mixing  of  the  entire 
stomach  contents  during  or  immediately  following  a  meal  is 
further  shown  by  the  experiments  of  Griitzner,  who  fed  rats 
with  foods  of  different  colors  and  on  kilHng  the  animals  and 

examining  the  stomach  con- 
tents found  that  the  portions 
which  had  been  eaten  succes- 
sively were  arranged  in  definite 
strata.  The  food  which  had 
been  first  eaten  lay  next  to  the 

walls  of  the  stomach  and  filled 
Fig    2. -Section  of  frozen  stomach      ^^^         j^^-^  •  ^^^^-^^   ^^^ 

of  rat  dunng  digestion  to  show  the  "^  -^  07 

stratification  of  food  given  at  differ-     succeeding  portions  were  ar- 

ent    times.     {Griitzner.)     The  food 

was  given  in  three  portions  and     ranged  regularly  in  the  interior 

colored     differently        Reproduced       -^    ^    concentric    fashion.      In 
from    Howell  s   Textbook   oj   Physi- 
ology, pubUshed  by  the  W.  B.  Saun-     describing  this  result  Howell 
ders  Co. 

says:  "Such  an  arrangement 
of  the  food  is  more  readily  understood  when  one  recalls  that 
the  stomach  has  never  any  empty  space  within ;  its  cavity 
is  only  as  large  as  its  contents,  so  that  the  first  portion  of 
food  eaten  entirely  fills  it,  and  successive  portions  find  the 
wall  layer  occupied  and  are  therefore  received  into  the  in- 
terior. The  ingestion  of  much  liquid  must  interfere  some- 
what with  this  stratification." 

In  considering  the  mechanism  of  gastric  digestion  it  is  con- 


THE    COURSE    OF   THE    FOOD  59 

venient  to  regard  the  stomach  as  having  three  regions  of 
somewhat  different  characteristics :  (i)  the  cardiac  end,  or 
fundus,  which  the  food  enters  when  swallowed ;  (2)  a  middle  . 
region  usually  considered  as  belonging  also  to  the  fundus ;  and 
(3)  the  pyloric  part,  terminating  at  the  pylorus  through  which 
the  food  passes  from  the  stomach  to  the  small  intestine. 
Certain  cells  of  the  stomach  wall  in  all  three  regions  have  the 
power  of  secreting  gastric  juice,  but  the  character  of  the  se- 
cretion, especially  as  regards  its  acidity,  varies  considerably 
in  the  different  parts.  In  the  middle  region  the  secretion  is 
rich  in  acid,  while  both  in  the  cardiac  region  and  at  the  ex- 
treme pyloric  end,  the  "border  cells"  or  "cover  cells"  (from 
which  the  secretion  of  the  acid  appears  to  take  place)  are 
few  in  number  or  entirely  lacking,  and  the  juice  secreted  in 
these  regions  may  be  neutral  or,  according  to  Howell,  even 
slightly  alkaline. 

The  nature  and  extent  of  the  muscular  movements  also 
vary  greatly  in  the  different  regions  of  the  stomach.  The 
peristaltic  waves  of  muscular  constriction  which  bring  about 
the  thorough  mixing  of  the  food  with  the  gastric  juice  begin 
in  the  middle  region  and  travel  toward  the  pylorus.  Over 
the  pyloric  part  of  the  stomach  (that  portion  which  is  pos- 
terior to  the  "transverse  band"),  when  food  is  present,  con- 
striction waves  are  continually  coursing  toward  the  pylorus. 
The  food  in  this  portion  is  first  pushed  forward  by  the  run- 
ning wave  and  then  by  pressure  of  the  stomach  wall  is  re- 
turned through  the  ring  of  constriction.     Thus  the  food  in  this 


6o  CHEMISTRY   OF   FOOD   AND    NUTRITION 

portion  of  the  stomach  is  thoroughly  mixed  with  the  gastric 
juice  and  is  forced  by  an  oscillating  progress  toward  the 
pylorus. 

The  food  in  the  cardiac  end  of  the  stomach  is  not  moved 
by  peristalsis,  and  so  comes  only  slowly  into  contact  with  the 
gastric  juice ;  and  since  the  juice  secreted  here  contains  little 
if  any  free  acid,  a  large  part  of  the  food  mass  remains  for 
some  time  (variously  estimated  at  from  30  minutes  to  2 
hours  or  more)  in  approximately  the  same  faintly  alkaline 
condition  in  which  it  was  swallowed,  and  salivary  digestion 
continues  in  this  part  of  the  stomach  without  interruption. 
Thus,  if  the  food  has  been  thoroughly  subdivided  and  mixed 
with  saliva  before  swallowing,  much  if  not  most  of  its  starch 
may  be  converted  into  dextrin  and  maltose  in  the  cardiac 
region  of  the  stomach  before  the  activity  of  the  ptyalin  is 
stopped  by  contact  with  the  acid  of  the  gastric  juice. 

The  fundus,  however,  is  not  entirely  inactive,  but  acts  as 
a  sort  of  reservoir  which  is  distended  by  and  slowly  contracts 
upon  the  food  mass,  thus  gradually  tending  to  move  the 
posterior  portions  and  particularly  the  more  fluid  portion  into 
the  pyloric  region.  As  digestion  proceeds,  the  pylorus  opens 
more  frequently  and  the  stomach  tends  to  empty  itself  more 
and  more  freely,  until  at  the  very  end  of  gastric  digestion  the 
pylorus  may  open  to  allow  the  passage  of  particles  which  have 
not  been  acted  upon  by  the  gastric  juice.  Whether  the 
stomach  will  thus  completely  empty  itself  of  one  meal  before 
the  eating  of  the  next  will  depend  of  course  upon  the  length 


THE    COURSE    OF    THE    FOOD  01 

of  the  interval  and  the  amount  and  character  of  the  food 
composing  the  meal. 

The  time  required  for  complete  passage  of  the  food  from 
the  stomach  probably  varies  greatly  with  circumstances. 
Small  test  meals  may  disappear  in  from  i  to  4  hours,  but 
in  cases  in  which  a  dog  or  a  pig  has  been  fed  500  grams  of 
lean  meat  at  a  time,  at  least  1 2  hours  have  elapsed  before  the 
entire  disappearance  of  the  food  from  the  stomach.  In 
experiments  upon  men,  test  meals  less  abundant  than  an 
ordinary  hearty  dinner  have  disappeared  entirely  from  the 
stomach  only  after  7  hours. 

In  studying  the  passage  of  food  from  the  stomach  into  tne 
intestine  Cannon  found  that  the  pylorus  does  not  open  at  the 
approach  of  each  wave  of  constriction  which  passes  over  this 
part  of  the  stomach,  but  only  at  irregular  intervals.  When 
the  observations  made  by  means  of  the  Roentgen  rays  were 
supplemented  by  chemical  examinations  of  stomach  and 
intestinal  contents  removed  at  different  stages,  it  appeared 
that  the  presence  of  free  acid  in  the  pyloric  part  of  the  stomach 
causes  the  pylorus  to  open,  and  its  presence  in  the  small 
intestine  causes  the  pylorus  to  close.  Thus  it  would  appear 
that  under  normal  conditions  it  is  only  when  the  protein  of 
the  food  has  become  more  or  less  completely  saturated  with 
hydrochloric  acid  and  some  of  the  latter  remains  in  the  free 
state,  that  the  food  is  allowed  to  pass  into  the  intestine. 
Ordinarily,  when  each  is  fed  separately,  protein  food  stays 
longer  in  the  stomach  than  carbohydrate,  and  this  is  doubt- 


62  CHEMISTRY   OF   FOOD    AND   NUTRITION 

less  due  to  the  combination  of  the  acid  of  the  gastric  juice 
with  the  protein  of  the  food  delaying  the  appearance  of  free 
acid  at  the  pylorus;  for  when  protein  food  was  acidulated 
before  feeding  and  carbohydrate  food  was  made  alkaline,  the 
protein  was  found  to  leave  the  stomach  more  rapidly  than  the 
carbohydrate.  That  the  passage  of  food  from  stomach  to 
intestine  is  governed  mainly  by  the  degree  of  acidity  reached 
in  the  pyloric  part  of  the  stomach  is  a  strong  indication  of 
the  importance  to  the  organism  of  the  action  of  the  acidity 
of  the  gastric  juice  in  effecting  a  partial  disinfection  of  the 
food  aside  from  its  digestive  action.  It  will  be  seen  also  that 
the  acidity  of  the  chyme  as  it  passes  the  pylorus  has  an 
important  influence  upon  the  secretion  of  the  pancreatic 
juice. 

The  gastric  juice  as  obtained  through  a  stomach  fistula 
is  of  course  the  mixed  secretion  of  the  glands  in  the  different 
regions  of  the  stomach  wall.  It  is  a  thin,  colorless  or  nearly 
colorless  liquid  whose  most  important  characteristics  are  the 
presence  of  free  hydrochloric  acid  and  of  pepsin.  While 
other  acids  may  be  foxmd  in  stomach  contents,  the  acidity  of 
gastric  juice  appears  to  be  due  entirely  to  hydrochloric  acid. 
Normal  human  gastric  juice  contains  about  0.2  to  0.3  per 
cent  of  free  hydrochloric  acid.  The  stimuU  which  bring  about 
secretion  of  gastric  juice  are  both  psychical  and  chemical. 
Psychical  stimulation  results  from  the  sensations  of  eating 
and  may  also  be  due  to  the  sight  and  odor  of  food.  The 
psychical  secretion  is  studied  chiefly  by  means  of  the  fictitious 


THE   COURSE   OF   THE   FOOD  63 

—  or  sham  —  feeding  experiments  in  which  food  is  given 
to  dogs  which  have  been  prepared  with  esophageal  openings 
through  which  the  swallowed  food  escapes  without  entering 
the  stomach.  When  such  a  dog  is  fed  with  meat,  for  ex- 
ample, there  is  a  considerable  secretion  of  gastric  juice  in 
spite  of  the  fact  that  no  food  reaches  the  stomach.  Such 
a  flow  of  gastric  juice  is  due  to  impulses  received  through 
the  nervous  system  and  specifically  through  the  vagus  nerve, 
for  fictitious  feeding  has  been  found  to  cause  a  flow  of  gastric 
juice  when  the  vagi  are  intact,  l^ut  not  after  they  have  been 
cut.  Secretion  produced  in  this  way  reflexly  as  the  result  of 
the  sensation  of  taste,  odor,  etc.,  is  called  by  Pawlow  a 
"psychic  secretion"  or  "appetite  juice."  When  the  secre- 
tion is  once  started,  even  if  no  food  enters  the  stomach,  the 
flow  of  juice  may  continue  for  some  time  after  the  stimulus 
has  ceased. 

Similar  observations  have  been  made  upon  a  boy  who  had 
a  stricture  of  the  esophagus  and  a  fistula  in  the  stomach. 
Food  when  chewed  and  swallowed  did  not  reach  the  stomach, 
but  was  regurgitated;  yet  it  caused  an  active  secretion  of 
gastric  juice  (Howell). 

In  an  ordinary  meal  the  psychic  secretion  insures  the 
beginning  of  gastric  digestion.  Stimulations  arising  within 
the  stomach  itself  supplement  the  psychic  influences  and 
provide  for  the  continued  secretion  of  the  gastric  juice  long 
after  the  mental  efTects  of  a  meal  have  disappeared.  This 
second  stimulation  is  chemical  and  depends  upon  the  pro- 


64  CHEMISTRY   OF   FOOD   AND   NUTRITION 

duction  in  the  pyloric  mucous  membrane  of  a  specific  sub- 
stance, or  hormone  J  which  acts  as  a  chemical  messenger  to  all 
parts  of  the  stomach,  being  absorbed  into  the  blood  and 
thence  exciting  the  activity  of  the  various  secreting  cells  of 
the  gastric  glands  (Stariing).  Meat  extracts,  soups,  etc., 
are  particulariy  active  in  exciting  the  secretion  which 
depends  upon  chemical  stimulation ;  milk  causes  less  secre- 
tion;  white  of  egg  is  said  to  have  no  effect. 

Under  normal  conditions,  the  amount  of  nutritive  mate- 
rial absorbed  from  the  stomach  is  insignificant  as  compared 
with  the  amount  absorbed  from  the  intestine.  Nearly  all 
the  food  eaten  is  passed  from  the  stomach  into  the  intestine 
in  the  form  of  chyme,  having  been  more  or  less  perfectly 
liquefied  and  acidulated  by  its  thorough  mixing  with  the 
gastric  juice  in  the  middle  and  pyloric  regions  of  the  stomach. 

Digestion  in  the  S?nall  Intestine.  —  It  has  been  seen  that 
the  pylorus  does  not  open  at  the  approach  of  each  wave 
of  constriction  of  the  stomach  wall,  but  only  at  intervals. 
When  it  opens,  food,  now  reduced  to  hquid  chyme,  is 
projected  into  the  upper  part  of  the  small  intestine.  Care- 
ful watching  of  this  food  shows  that  usually  it  Ues  for  some 
time  in  the  curve  of  the  duodenum,  until  several  additions 
have  been  made  to  it  from  the  stomach  and  a  long  thin  string 
of  food  material  is  formed.  WTiile  the  food  rests  here  the 
bile  and  pancreatic  juice  are  poured  out  upon  it,  and  here 
also,  as  well  as  in  other  parts  of  the  small  intestine,  a  certain 
amount  of  intestinal  digestive  juice   ("succus  entericus") 


THE    COURSE    OF   THE   FOOD  65 

is  secreted  by  the  glands  of  the  lining  membrane  and  mixed 
with  the  intestinal  contents.  While  for  purposes  of  descrip- 
tion the  pancreatic  and  intestinal  juices  and  the  bile  may  be 
discussed  separately,  it  is  to  be  remembered  that  in  normal 
digestion  they  always  act  together.  Cannon's  observations 
showed  that  after  a  certain  amount  of  food  and  digestive 
juices  has  accumulated  as  just  described  in  the  first  loop  of 
the  small  intestine,  the  mass  all  at  once  becomes  segmented 
by  constrictions  of  the  intestinal  walls,  and  the  segmen- 
tation is  repeated  rhythmically  for  several  minutes,  thoroughly 
mixing  the  digestive  juices  with  the  food. 

In  this  part  of  the  intestine  the  alternate  positions  of  the 
segments  are  sometimes  far  apart,  so  that  the  individual 
portions  are  subjected  to  relatively  extensive  and  energetic 
to-and-fro  movement,  which  is  doubtless  very  important, 
not  only  in  securing  thorough  mixing  of  the  food  with  the 
secretions,  but  especially  in  facilitating  the  emulsification  of 
fat. 

Finally  the  segments  unite  into  a  single  mass  or  form  in 
groups  and  begin  to  move  forward.  The  peristalsis  here  is 
much  more  rapid  than  that  which  normally  occurs  further 
along  in  the  intestine.  The  masses  go  forward  swiftly  and 
continuously  for  some  distance,  and  then  begin  to  collect  in 
thicker  and  longer  strings  which  are  seen  characteristically 
in  the  other  coils  of  the  small  intestine. 

The  activity  most  commonly  seen  by  Cannon  in  these 
coils  is  the  simultaneous  division  of  the  food  mass  in  any 


66  CHEMISTRY    OF   FOOD    AND   NUTRITION 

given  coil,  into  small  segments,  and  a  rythmic  repetition  of  the 
segmentation  —  in  cats,  at  the  rate  of  30  segmentations  per 
minute.  The  effects  of  the  muscular  constrictions  which 
cause  the  segmentation  are  (i)  a  further  mixing  of  food  and 
digestive  juices,  (2)  the  bringing  of  the  digested  food  into 
contact  with  the  absorbing  membrane,  (3)  the  emptying  of 
the  venous  and  lymphatic  radicles  in  the  membrane,  the 
material  which  they  have  absorbed  being  forced  into  the 
veins  and  lymph  vessels  by  the  compression  of  the  intestinal 
wall.  After  a  varying  length  of  time  the  segmentation 
ceases  and  the  small  segments  are  carried  forward  individ- 
ually by  the  peristaltic  movement,  or  join  and  move  on  as  a 
single  body. 

The  fluid  food  mass  which  the  stomach  pours  into  the 
duodenum  contains  a  small  amount  of  free  hydrochloric  acid 
besides  a  larger  amount  combined  with  protein  and  some- 
times organic  acids  from  the  food  as  eaten,  or  from  bacterial 
fermentation  of  carbohydrates  in  the  stomach.  The  pylorus 
having  closed,  the  alkalinity  of  the  bile,  the  pancreatic  juice, 
and  the  intestinal  juice  combine  to  neutralize  the  acids  present. 

In  man  the  main  duct  of  the  pancreas  (duct  of  Wirsung)  and 
the  common  bile  duct  unite  and  empty  into  the  small  intes- 
tine about  8  to  10  cm.  (3  to  4  inches)  below  the  pylorus. 
The  pancreatic  juice  is  a  clear  liquid  having  an  alkalinity 
probably  equivalent  to  a  0.5  per  cent  solution  of  sodium 
carbonate  and  containing  three  important  enzymes  or  their 
zymogens  —  trypsin,  amylopsin,  and  steapsin  or  lipase. 


THE    COURSE    OF    THE   FOOD  67 

The  rate  of  flow  of  the  pancreatic  juice  varies  with  the' 
period  of  digestion  and  is  to  some  extent  dependent  upon  the 
nature  of  the  food.  After  a  meal  of  bread  alone  the  maxi- 
mum secretion  occurs  earlier  than  after  a  meal  of  meat, 
probably  because  carbohydrate  food  is  passed  from  the  stom- 
ach into  the  intestine  more  rapidly  than  is  protein  food.  It 
is  stated  that  the  composition  of  the  pancreatic  juice  varies 
with,  and  tends  to  adapt  itself  to,  the  character  of  the  food 
eaten ;  but  the  suggestion  has  not  been  thoroughly  worked 
out.  Acids  brought  in  contact  with  the  mucous  membrane 
of  the  duodenum  result  in  a  stimulation  of  the  secretion  of  the 
pancreatic  juice.  This  action  begins  at  once  when  any  of  the 
acid  stomach  contents  passes  through  the  pylorus,  and  has 
been  shown  by  Bayliss  and  Starling  to  be  due  to  a  definite 
chemical  substance,  secretin,  a  typical  hormone  produced 
as  the  result  of  the  action  of  the  acid  upon  some  constituent 
of  the  intestinal  mucous  membrane,  which  is  absorbed  and 
carried  by  the  blood  to  the  pancreas  and  there  stimulates 
the  flow  of  pancreatic  juice.  A  concise  and  interesting  ac- 
count of  the  discovery  and  significance  of  secretin  is  given  by 
Starling  in  his  Recent  Advances  in  the  Physiology  of  Diges- 
tion, pp.  85-93.  Starling  considers  that  the  chemical, 
mechanism,  namely,  the  formation  of  hormones  and  their 
circulation  through  the  blood  to  the  reactive  tissue,  suffices 
to  account  for  the  whole  of  the  activity  of  the  pancreas,  and 
that  it  is  doubtful  whether  the  nervous  system  plays  any  part 
in  this  activity. 


68  CHEMISTRY    OF   FOOD   AND   NUTRITION 

Human  bile,  which,  as  aheady  stated,  enters  the  intestine 
through  the  same  duct  with  the  pancreatic  juice,  is  a  sHghtly 
alkaline  solution  containing,  in  addition  to  water  and  salts, 
bile  pigments,  bile  acids  (as  salts),  cholesterin,  lecithin,  and  a 
peculiar  protein  derived  from  the  mucous  membrane  of  the 
bile  ducts  and  gall  bladder.  The  presence  of  the  bile  in  the 
intestinal  contents  greatly  increases  the  solubility  of  the 
fatty  acids,  while  at  the  same  time  it  diminishes  the  surface 
tension  between  watery  and  oily  fluids.  Thus  bile  aids  the 
digestion  of  proteins  and  carbohydrates  and  both  the  diges- 
tion and  the  absorption  of  fats.  The  bile  acids  are  themselves 
absorbed  to  a  considerable  extent  and  again  secreted  by  the 
liver.  The  secretion  of  bile  by  the  liver,  although  variable 
in  amount,  is  continuous.  Its  ejection  from  the  gall  bladder 
into  the  intestine  occurs,  however,  only  during  digestion,  and 
appears  to  be  excited  by  the  passage  of  chyme  through  the 
pylorus,  and  to  run  parallel  to  the  outpouring  of  the  pan- 
creatic juice.  According  to  Starling,  the  rapid  flow  of  bile 
during  intestinal  digestion  is  due  not  only  to  the  pouring  out 
of  what  was  previously  stored  in  the  gall  bladder,  but  also  to 
an  increased  rate  of  secretion  to  which  the  liver  is  stimulated 
by  the  same  chemical  mechanism  which  stim^ulates  the  flow 
of  pancreatic  juice. 

The  intestinal  jtftce  is  a  distinctly  alkaline  liquid  secreted 
by  the  tubular  glands  (crypts  of  Lieberkiihn)  with  which 
the  small  intestine  is  hned.  It  contains  at  least  five  en- 
zymes :  enterokinase,  by  the  action  of  which  trypsinogen  is 


THE    COURSE    OF    THE    FOOD  69 

converted  into  trypsin;  erepsin,  which  produces  further 
cleavage  of  the  proteoses  and  peptones;  and  the  three  en- 
zymes, invertase  (or  invertin),  maltase,  and  lactase,  which 
hydrolyze  respectively  the  three  disaccharides,  sucrose, 
maltose,  and  lactose.  The  secretion  of  intestinal  juice  is 
probably  stimulated  by  secretin,  and  possibly  also  by  another 
hormone  whose  production  is  dependent  upon  the  presence 
of  pancreatic  juice. 

The  very  discordant  statements  which  have  been  made 
regarding  the  reaction  of  the  contents  of  the  small  intestine 
are  no  doubt  largely  due  to  the  failure  of  observers  to  take 
account  of  the  differing  behavior  of  the  various  indicators. 
Careful  observations  were  made  by  Moore  and  Bergin  in  1897. 
Samples  taken  through  a  fistula  immediately  above  the 
ileoc£Ecal  valve  were  always  alkaline  to  methyl-orange,  lac- 
moid,  and  litmus,  but  acid  to  phenolphthalein.  Hence  neither 
hydrochloric  acid,  nor  any  appreciable  amount  of  the  stronger 
organic  acids  such  as  acetic,  butyric,  or  lactic,  could  have  been 
present  in  the  free  state.  The  acid  reaction  shown  by  phe- 
nolphthalein was  probably  due  either  to  traces  of  organic  acids, 
or  possibly  to  dissolved  carbonic  acid,  or  to  acid-protein  com- 
pounds not  yet  completely  digested  and  absorbed.  It  seems 
probable  that  this  fairly  represents  the  condition  as  to  reaction 
which  exists  throughout  the  greater  part  of  the  small  intes- 
tine. Under  such  conditions  all  three  classes  of  foodstuffs 
would  be  readily  attacked  by  the  digestive  enzymes  present, 
and  brought  into  condition  for  absorption. 


70  CHEMISTRY    OF   FOOD   AND    NUTRITION 

Absorption  takes  place  very  readily  in  the  small  intestine 
—  more  readily  and  completely  than  can  be  explained  by 
the  purely  mechanical  laws  of  diffusion.  Thus  if  blood  serum 
were  introduced  into  an  isolated  loop  of  small  intestine,  it 
should,  according  to  mechanical  analogy,  have  no  tendency 
to  pass  through  the  intestinal  wall,  since  the  fluid  on  the  two 
sides  of  this  wall  would  then  be  of  the  same  nature ;  yet  in 
such  experiments  almost  complete  absorption  is  found  to  take 
place.  It  has  also  been  found  that  the  rapidity  of  absorption 
of  salts  from  the  intestine  stands  in  no  direct  relation  to  their 
diffusion  velocity  (Wallace  and  Gushing).  When  the  in- 
testinal wall  is  injured  by  the  action  of  sodium  fluoride  or 
potassium  arsenate,  its  absorption  power  is  diminished,  and 
absorption  then  follows  the  laws  of  diffusion  and  osmosis 
(Howell).  On  account  of  these  facts  the  normal  process  is 
sometimes  called  "resorption"  to  distinguish  it  from  the 
passive  process  of  absorption  which  takes  place  with  a  dead 
or  poisoned  membrane. 

Observations  have  been  made  upon  a  patient  having  a 
fistula  at  the  end  of  the  small  intestine.  In  this  case  it  was 
found  that  85  per  cent  of  the  protein  matter  of  the  food  was 
absorbed  before  this  point  was  reached,  and  the  absorption 
of  the  other  foodstuffs  is  probably  equally  complete.  For 
this  patient  the  food  began  to  pass  the  ileocaecal  valve  in  from 
2  to  5i  hours  after  eating,  but  the  time  required  from  the 
eating  of  the  food  until  the  last  portions  had  passed  into  the 
large  intestine  was  9  to  22,  hours. 


THE    COURSE    OF   THE   FOOD  7 1 

The  rate  of  passage  of  different  foodstuffs  from  the  stomach 
and  through  the  small  intestine  has  been  studied  by  Cannon 
with  the  aid  of  the  Roentgen  rays,  according  to  the  general 
method  already  described.  Fat,  carbohydrate,  and  protein 
foods,  uniform  in  consistency  and  in  amount  (25  cc),  were 
fed  to  cats  which  had  been  fasted  for  24  hours.  At  regular 
intervals  for  7  hours  after  feeding,  the  shadows  of  the  stomach 
and  intestinal  contents  were  observed  by  means  of  the  Roent- 
gen rays.  It  was  found  that,  when  fats  were  fed  alone,  the 
discharge  of  fat  from  the  stomach  began  slowly  and  con- 
tinued at  nearly  the  same  rate  at  which  it  left  the  small  intes- 
tine by  absorption  and  by  passage  into  the  large  intestine, 
so  that  there  was  never  any  great  accumulation  of  fat  in  the 
small  intestine  where  its  emulsification  and  digestion  chiefly 
take  place.  Carbohydrate  foods  (fed  alone)  began  to  leave 
the  stomach  much  earlier  and  passed  out  more  rapidly. 
Proteins  frequently  did  not  begin  to  leave  the  stomach  during 
the  first  half  hour,  and  in  general  a  meal  of  proteins  remained  in 
the  stomach  about  twice  as  long  as  a  meal  of  carbohydrates. 
When  carbohydrates  were  fed  first  and  proteins  immediately 
after,  the  presence  of  the  proteins  in  the  cardiac  end  of  the 
stomach  did  not  materially  check  the  departure  of  the  car- 
bohydrate food  lying  at  the  pylorus ;  but  when  proteins 
were  fed  first,  their  presence  in  the  pyloric  region  delayed 
considerably  the  onward  passage  of  any  carbohydrate  which 
may  have  been  swallowed  later.  When  protein  and  carbo- 
hydrates were  mixed  in  equal  parts  before  feeding,  the  mixture 


72  CHEMISTRY    OF   FOOD   AND    NUTRITION 

passed  through  the  stomach  more  rapidly  than  protein  alone 
and  less  rapidly  than  carbohydrate.  Either  protein  or 
carbohydrate  when  mixed  with  fat  passed  out  of  the  stomach 
more  slowly  than  when  fed  alone.  The  process  of  rhythmic 
segmentation  above  described  was  seen  with  all  three  kinds  of 
foodstuffs,  and  the  frequency  of  its  occurrence  corresponded 
roughly  to  the  amount  of  food  present  in  the  intestine.  The 
interval  between  the  feeding  and  the  first  appearance  of  food 
in  the  large  intestine  was  variable,  but  in  these  experiments 
with  cats  the  mean  for  carbohydrates  was  about  4  hours,  for 
proteins  about  6  hours,  and  for  fats  about  5  hours. 

Digestion  in  the  Large  Intestine.  —  We  have  seen  that  in 
the  small  intestine  the  conditions  are  very  favorable  both 
for  digestion  and  for  absorption,  and  that  very  much  the 
greater  part  of  the  available  nutrients  has  been  absorbed 
before  the  food  mass  reaches  the  ileocaecal  valve.  It  may, 
however,  still  contain  incompletely  digested  food  and  active 
digestive  enzymes,  and  so  digestion  may  continue  in  the  large 
intestine.  Studying  the  behavior  of  the  food  mass  here  by 
the  same  methods  as  in  the  stomach  and  small  intestine, 
Cannon  finds  that  the  ileocaecal  valve  is  physiologically 
"  competent"  for  food  which  passes  through  it  normally  from 
the  small  intestine,  i.e.  the  food  which  has  reached  the  large 
intestine  in  the  natural  way  is  ordinarily  never  forced  back 
into  the  small  intestine  again.  This  is  important  because  in 
the  anterior  portion  of  the  large  intestine  the  waves  which 
appear  most  frequently  are  those  of  antiperistalsis  —  i.e. 


THE    COURSE    OF    THE    FOOD  73 

tend  to  force  the  food  back  toward  the  small  intestine.  Since 
the  ileocaecal  valve  prevents  the  food  passing  back,  these 
antiperistaltic  waves  result  in  thoroughly  churning  the  food 
in  this  part  of  the  large  intestine  and  constantly  bringing  fresh 
portions  in  contact  with  the  intestinal  wall  so  that  the  condi- 
tions here  are  still  favorable  for  absorption.  Moreover,  the 
walls  of  the  large  intestine  furnish  an  alkaline  secretion  which 
further  aids  the  completion  of  the  digestive  changes  already 
begun.  So  far  as  known,  the  large  intestine  secretes  no  diges- 
tive enzyme  of  its  own. 

The  material  which  has  passed  through  the  ileocaecal  valve 
remains  in  the  large  intestine  for  a  comparatively  long  time 
(generally  i  to  2  days  —  often  longer) ;  for  the  peristaltic 
movements  which  carry  the  material  onward,  while  stronger 
than  the  waves  of  antiperistalsis,  are  of  less  frequent  occur- 
rence, at  least  in  the  first  part  of  the  large  intestine.  During 
this  time  there  is  a  marked  absorption  of  water,  along  with  the 
remaining  products  of  digestion,  and  the  products  of  bac- 
terial activity.  The  residual  material  gradually  becomes 
more  solid  and  takes  on  the  character  of  feces. 

The  fecal  matter  passed  per  day  varies  considerably  in 
health,  but,  on  an  ordinary  mixed  diet  of  digestible  food 
materials,  is  usually  between  100  and  200  grams  of  fresh 
substance  containing  25  to  50  grams  of  solids.  The  feces 
contain  any  indigestible  substances  swallowed  with  the  food 
and  any  undigested  residues  of  true  food  material,  but 
ordinarily  they  appear  to  be  largely  composed  of  residues  of 


74  CHEMISTRY    OF   FOOD    AND   NUTRITION 

the  digestive  juices,  together  ^\^th  certain  substances  which 
have  been  formed  in  metabolism  and  excreted  by  way  of  the 
intestine,  and  the  bodies  of  bacteria,  most  of  which  are  apt 
to  be  dead  before  the  feces  are  passed. 

Prausnitz  studied  the  feces  of  6  persons  placed  alternately 
on  meat  and  on  rice  diets  and  found  that,  although  the  soHds 
of  the  meat  were  about  ten  times  as  rich  in  nitrogen  as  the 
solids  of  the  rice,  the  two  diets  yielded  feces  whose  soUds  were 
of  practically  the  same  composition.  Prausnitz  considers 
that  "normal"  feces  have  essentially  the  same  composition 
irrespective  of  the  food,  the  quantity  of  food  residues  in  such 
"normal"  feces  being  negligible.  From  this  point  of  view 
the  feces  show  not  so  much  the  extent  to  which  the  food  has 
been  absorbed  as  whether  it  is  a  large  or  a  small  feces-former. 
On  the  other  hand,  so  far  as  the  nitrogen  compounds  of  the 
feces  are  concerned,  it  is  probably  true,  as  generally  assumed, 
that  they  represent  material  either  lost  or  expended  in  the 
w^ork  of  digestion,  and  therefore  that  the  nitrogen  of  the  feces 
is  to  be  deducted  from  that  of  the  food  in  estimating  the 
amount  available  for  actual  tissue  metabolism.  This,  how- 
ever, is  by  no  means  equally  true  of  the  ash  constituents, 
many  of  which  after  being  metabolized  in  the  body  are  elimi- 
nated mainly  by  way  of  the  intestine  rather  than  through 
the  kidneys. 

The  feces  produced  in  fasting  have  been  found  to  contain 
about  2  to  4  grams  of  solids  including  o.i  to  0.3  gram  of  nitro- 
gen per  day.     On  a  diet  consisting  entirely  of  non-nitrogenous 


THE    COURSE    OF    THE    FOOD  75 

food  the  amount  of  nitrogen  in  the  daily  feces  was  0.5  to  0.9 
gram  per  day,  or  much  more  than  in  fasting,  and  also  more 
than  is  sometimes  found  in  feces  from  food  furnishing  enough 
protein  to  meet  all  the  needs  of  the  body.  Thus  the  expen- 
diture of  nitrogenous  material  in  the  digestion  of  fats  and 
carbohydrates  may  be  larger  than  in  the  digestion  of  protein 
food. 

The  feces  always  contain  fat  (or  at  least  substances  soluble 
in  ether)  as  well  as  protein.  Fasting  men  have  ehminated 
0.57  to  1.3  grams  of  fat  per  day;  and  when  the  diet  is  very 
poor  in  fat,  the  feces  may  contain  as  much  as  was  contained 
in  the  food.  As  the  fat  content  of  the  food  rises  the  actual 
amounts  in  the  feces  increase,  but  the  relative  amounts  de- 
crease, so  that  up  to  a  certain  point  the  apparent  percentage 
utilization  of  the  fat  becomes  higher.  The  limit  to  the 
amount  of  fat  which  can  be  thus  well  digested  varies  with  the 
individual  and  with  the  form  in  which  the  fat  is  given.  Quan- 
tities up  to  200  grams  per  day  have  been  absorbed  to  within 
2  to  3  per  cent  when  given  in  the  form  of  milk,  cheese,  or 
butter. 

In  addition  to  protein  and  fat  the  feces  always  contain 
various  other  forms  of  organic  matter  wliich  in  the  routine 
proximate  analyses  usually  made  in  connection  with  feeding 
experiments  are  collectively  reported  as  "carbohydrates 
determined  by  difference." 

With  these  facts  in  mind  one  may  make  use  of  the  so-called 
"coefficients  of  digestibility"  without  being  misled  by  them. 


76 


CHEMISTRY    OF    FOOD   AND    NUTRITION 


These  coefficients  show  the  relation  between  the  constituents 
of  the  food  consumed  and  the  corresponding  constituents  of 
the  feces.  Thus  if  the  feces  from  a  given  diet  contain  5 
per  cent  as  much  protein  as  was  contained  in  the  food,  this  pro- 
portion is  assumed  to  have  been  lost  or  expended  in  digestion, 
and  the  coefficient  of  digestibility  of  the  protein  of  the  diet  is 
stated  to  be  95  per  cent.  While  as  just  shown  this  assump- 
tion is  not  entirely  correct,  yet  it  is  approximately  true  of  the 
organic  nutrients  that  the  difference  ibetween  the  amounts  in 
the  food  and  in  the  feces  represent  what  is  available  to  the 
tissues  of  the  body,  and  thus  these  coefficients  serve  a  use- 
ful purpose  in  the  computation  of  the  nutritive  values  of 
foods. 

From  the  results  of  hundreds  of  digestion  experiments  At- 
water  computed  the  coefficients  of  digestibility  of  the  organic 
nutrients  of  the  main  groups  of  food  materials,  when  used 
by  man  as  part  of  a  mixed  diet,  to  be  as  follows :  — 

Coefficients  of  Digestibility  of  Foods  when  Used  in  Mixed  Diet 
(Atwater) 


Protein 

PER  CENT 

Fat 

PER   CENT 

Carbohydrates 

PER  CENT 

Animal  foods 

Cereals  and  breadstuffs    .     . 

Dried  legumes 

Vegetables 

Fruits 

Total  food  of  average  mixed 
diet 

97 
85 
78 
83 
85 

92 

95 

90 
90 
90 
90 

95 

98 
98 

97 
95 
90 

98 

THE    COURSE    OF    THE   FOOD  77 

In  some  cases  these  figures  are  higher  than  have  been  re- 
ported for  similar  foods  by  other  observers,  the  differences 
being  due  mainly  to  the  fact  (not  formerly  recognized)  that  a 
food  may  be  more  perfectly  utilized  when  fed  as  part  of  a 
simple  mixed  diet  than  when  fed  alone.  Milk  is  an  example 
of  such  a  food,  and  has  when  consumed  as  part  of  a  mixed 
diet  a  much  higher  coefficient  of  digestibility  than  is  often 
assigned  to  it  on  the  basis  of  earlier  experiments. 

It  will  be  seen  that  the  coefficients  differ  less  for  the  different 
t>pes  of  food  than  might  be  expected  from  popular  impressions 
of  "digestibility"  and  ''indigestibility."  It  is  also  note- 
worthy that  the  coefficients  of  digestibility  are  less  influenced 
by  the  conditions  under  which  the  food  is  eaten  and  vary  less 
with  individuals  than  is  generally  supposed. 

In  explanation  of  this  it  may  be  noted  that  general  impres- 
sions of  digestibility  relate  mainly  to  ease  of  digestion  and 
particularly  to  ease  and  rapidity  of  gastric  digestion,  and  that 
there  is  little  direct  relation  between  the  ease  with  which  a 
food  is  digested  in  the  stomach  and  the  extent  to  which  it  is 
ultimately  digested  in  its  passage  through  the  entire  digestive 
tract.  Substances  which  are  resistant  to  gastric  digestion 
will  tend  to  remain  long  in  the  stomach  and  will  probably 
excite  a  greater  flow  of  gastric  juice.  Thus  a  greater  amount 
of  acid  chyme  will  enter  the  duodenum,  and  this  will  result 
in  the  secretion  of  a  greater  amount  of  pancreatic  juice  also. 

Similarly  an  increase  in  the  amount  of  food  eaten  will 
increase  the  work  of  digestion,  but  may  have  little  effect  upon 


78  CHEMISTRY    OF   FOOD    AND   NUTRITION 

the  coefficient — the  percentage  of  the  ingested  foodstuff  which 
is  ultimately  absorbed.  In  a  series  of  four  experiments  by 
the  writer  the  diet  consisted  of  crackers  and  milk  in  uniform 
relative  proportions  throughout,  but  with  marked  variation 
in  the  amounts  eaten,  —  the  daily  diet  for  the  first  and  third 
experiments  being  150  grams  of  crackers  and  1500  grams  of 
milk,  and  for  the  second  and  fourth  experiments,  300  grams  of 
crackers  and  3000  grams  of  milk.  In  this  case  it  was  found 
that  the  doubHng  of  a  small  diet  decreased  the  coefficient  of 
digestibiHty  by  less  than  i  per  cent.  Snyder  reports  that  as 
between  medium  and  large  amounts  of  oatmeal  and  milk, 
the  protein  was  7  per  cent  and  the  fat  6  per  cent  more  com- 
pletely absorbed  in  the  case  of  the  medium  ration. 

Bacterial  Action  in  the  Digestive  Tract.  —  In  the  preceding 
we  have  considered  the  course  of  the  food  through  the  diges- 
tive tract  without  reference  to  the  presence  and  activities  of 
bacteria.  These  may,  however,  materially  modify  the  di- 
gestive process  in  certain  cases.  The  digestive  tract  of  an 
infant  contains  no  bacteria  at  birth,  but  usually  some  gain 
access  during  the  first  day  of  Ufe.  In  the  average  adult  it  is 
estimated  that  each  day's  food  in  its  passage  through  the 
digestive  tract  is  subjected  to  the  action  of  over  one  hundred 
biUion  bacteria. 

Since  bacteria  are  regularly  present  in  the  digestive  tract  in 
such  large  numbers,  it  has  been  questioned  whether  they  may 
not  perform  some  essential  function  in  connection  with  the 
normal  processes  of  digestion.     Experiments  to  demonstrate 


THE    COURSE    OF   THE   FOOD  79 

whether  animals  are  independent  of  such  bacteria  are  beset 
with  many  difficulties,  and  have  sometimes  led  to  the  belief 
that  bacteria  were  essential;  but  Nuttall  and  Thierfelder 
kept  sterile  for  several  days  the  digestive  tracts  of  young 
guinea  pigs  delivered  by  Caesarian  section  and  fed  upon 
thoroughly  sterilized  food,  and  as  the  animals  thus  treated 
lived  and  gained  in  weight,  the  experimenters  concluded  that 
intestinal  bacteria  are  not  essential  to  normal  nutrition. 
This  view  has  recently  received  strong  support  from  the  ob- 
servations of  Levin,  who  examined  the  intestinal  contents  of 
Arctic  animals  in  Spitzenberg.  The  digestive  tracts  of  white 
bears,  seals,  reindeer,  eider  ducks,  arid  penguin  were  found 
to  be  in  most  cases  free  from  bacteria,  showing  that  the  latter 
are  not  essential  to  the  normal  processes  of  digestion  and 
nutrition. 

If  it  were  possible  to  exclude  absolutely  all  bacteria  from  the 
digestive  tract,  it  is  probable  that  the  well-being  of  the  body 
would  be  in  no  wise  impaired ;  'y^t  under  such  conditions  as 
ordinarily  exist,  the  bacteria  which  usually  predominate  in  the 
digestive  tract  of  the  healthy  man  probably  render  an  im- 
portant service  in  helping  to  protect  the  body  against  occa- 
sional invasions  of  obnoxious  species. 

A  few  species,  such  as  B.  lactis  aerogenes,  B.  coli,  B.  bifidus, 
have  adapted  themselves  so  well  to  the  conditions  existing 
in  the  human  digestive  tract  that  they  are  ordinarily  not  harm- 
ful to  the  host  unless  present  in  abnormally  large  numbers, 
and  being  able  to  hold  their  own  against  newcomers  they  are 


So  CHEMISTRY    OF   FOOD   AND    NUTRITION 

occasionally  able  to  do  a  distinct  service  by  gi\dng  rise  to 
conditions  which  check  the  development  of  other  types  of 
organisms,  capable  of  doing  injury,  which  under  ordinary 
conditions  man  can  hardly  prevent  from  occasionally  gaining 
ingress  through  food  or  drink. 

According  to  Herter:  "The  presence  in  the  colon  of  im- 
mense numbers  of  obHgate  micro-organisms  of  the  B.  coli 
type  may  be  an  important  defense  of  the  organism  in  the 
sense  that  they  hinder  the  development  of  that  putrefactive 
decomposition  which,  if  prolonged,  is  so  injurious  to  the  organ- 
ism as  a  whole.  We  have  in  this  adaptation  the  most  rational 
explanation  of  the  meaning  of  the  myriads  of  colon  bacilli 
that  inhabit  the  large  intestine.  This  \'iew  is  not  inconsistent 
with  the  conception  that  under  some  conditions  the  colon 
bacilli  multiply  to  such  an  extent  as  to  prove  harmful  through 
the  part  they  take  in  promoting  fermentation  and  putre- 
faction." 

If  for  our  present  purpose  we  consider  only  the  bacteria 
w^hich  are  prominent  in  producing  decomposition  of  food- 
stuffs in  the  digestive  tract,  and  these  only  with  reference  to 
this  one  property,  we  may  regard  as  the  three  main  types : 
(i)  the  bacteria  of  fermentation,  such  for  example  as  the  lac- 
tic acid  bacteria ;  (2)  the  putrefactive  bacteria,  such  as  the 
anaerobic  B.  aero  genes  capulatus;  (3)  bacteria  of  the  B.  coli 
type,  showing  some  of  the  characters  of  both  the  fermenta- 
tive and  putrefactive  types,  but  tending  in  general  to  antago- 
nize the  putrefactive  anaerobes. 


THE    COURSE    OF    THE    FOOD  8 1 

Among  cases  of  excessive  bacterial  decomposition  in  the 
digestive  tract  the  fermentation  of  carbohydrates  with  pro- 
duction of  organic  acids  (and  possibly  also  alcohol)  is  most 
likely  to  occur  in  the  stomach,  while  the  putrefaction  of  pro- 
teins occurs  mainly  in  the  large  intestine.  While  it  is  true 
that  the  products  of  fermentation  tend  to  restrict  putrefac- 
tion, yet,  since  the  two  processes  take  place  for  the  most  part 
at  such  widely  separated  points  of  the  digestive  tract,  there 
may  be  excessive  fermentation  and  excessive  putrefaction  in 
the  same  individual  at  the  same  time.  Among  the  conditions 
which  favor  excessive  fermentation  are :  diminished  tone  and 
motility  of  the  stomach,  dilation,  diminution  or  absence  of 
free  hydrochloric  acid  in  the  gastric  juice,  and  excessive  use 
of  carbohydrate  food — especially  sucrose  and  glucose,  which 
are  more  susceptible  to  fermentation  in  the  stomach  than 
are  lactose  and  starch. 

In  the  normal  human  stomach  the  conditions  are  quite 
unfavorable  for  the  development  of  anaerobic  putrefactive 
bacteria,  not  only  because  of  the  presence  of  air,  but  also  owing 
to  the  action  of  the  gastric  juice;  and  favorable  conditions  are 
not  found  in  the  anterior  portion  of  the  small  intestine.  In 
the  lower  third  of  the  small  intestine  the  numbers  of  bacteria 
increase  and  among  them  sometimes  putrefactive  forms.  In 
the  large  intestine  the  conditions  are  much  more  favorable 
for  the  anaerobic  putrefactive  bacteria,  and  these  may  produce 
marked  decomposition  in  any  protein  still  remaining  unab- 
sorbed.     In  general  the  greater  the  amount  of  digestible  but 


82  CHEMISTRY    OF   FOOD    AND    NUTRITION 

undigested  or  unabsorbed  protein  and  the  longer  the  material 
stays  in  the  large  intestine,  the  greater  the  amount  of  putre- 
factive decomposition.  Not  infrequently  excessive  fermen- 
tation in  the  stomach  causes  local  sensitiveness  which  results 
in  the  taking  of  less  bulky  food  (or  such  as  has  less  indiges- 
tible residue),  which  in  turn  tends  to  stagnate  in  the  intestine 
and  thus  render  the  conditions  more  favorable  for  intestinal 
putrefaction.  According  to  Herter  there  sometimes  results 
from  the  eating  of  large  quantities  of  meat  and  sugar  a  type 
of  fermentation  in  which  oxalic  acid  is  produced  and  which 
must  therefore  be  highly  injurious;  but  ordinarily  the  products 
of  fermentation  are  only  irritating,  while  putrefaction  gives 
rise  to  products  which  are  more  distinctly  toxic.  These  in- 
clude indol,  skatol,  phenol,  and  cresol,  which  are  for  the  most 
part  absorbed  into  the  system  and  finally  execreted  in  com- 
bination with  sulphuric  acid  as  "ethereal"  or  "conjugated  " 
sulphates.  Of  these  the  best  known  is  potassium  indoxyl 
sulphate,  commonly  known  as  "indican."  The  amounts  of 
conjugated  sulphates  and  of  indican  in  the  urine  are  valuable 
indications  of  the  intensity  of  the  putrefactive  process  in  the 
intestine. 

REFERENCES 

Cannon.  The  Movements  of  the  Stomach  studied  by  Means  of  the 
Roentgen  Rays.    American  Journal  of  Physiology,  i,  259. 

The  Movements  of  the  Intestines  studied  by  Means  of  the  Roentgen 

Rays.    American  Journal  of  Physiology,  6,  251. 

Salivary  Digestion  in  the  Stomach.   A  merican  Journal  of  Physiology, 

9,  396. 


THE   COURSE    OF   THE   FOOD  83 

Cannon.     The  Passage  of  Diflferent  Foodstuffs  from  the  Stomach  and 
through  the  Small  Intestine.     American  Journal  of  Physiology,  12, 

387. 
The  Acid  Control  of  the  Pylorus.    American  Journal  of  Physiology, 

20, 283. 
Fischer.     Physiology  of  Alimentation  (1907). 
Gerhardt.     Ueber    Darmfaulnis.     Ergebnisse    der    Physiologic,   3,    I, 

107-154  (1904). 
Herter.     Chemical  Pathology  (1902). 

Bacterial  Infections  of  the  Digestive  Tract  (1907). 

Howell.     Textbook  of  Physiology,  2d  ed.  (1907). 

Oppenheimer.     Handbuch  der  Biochemie,  Vol.  3,  Part  2  (1909). 

Pawlow.     The  Work  of  the  Digestive  Glands  (1910). 

Schaefer.     Textbook  of  Physiology  (1898). 

Schmidt  and  Strassburger.   Die  Faezes  des  Menschen  im  normalen  und 

krankhaften  Zustande,  2d  edition  (1905). 
Starling.     Recent  Advances  in  the  Physiology  of  Digestion  (1907). 


CHAPTER    IV 

THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM 

CARBOHYDRATES 

As  soon  as  the  saliva  becomes  mixed  with  the  food  its  amy- 
lase (ptyalin)  begins  to  act  upon  the  starch  and  dextrin,  and 
this  action  continues,  as  has  been  explained,  for  some  time  after 
the  food  reaches  the  stomach,  and  normally  it  doubtless  re- 
sults in  the  digestion  by  the  saliva  of  a  large  proportion  of  the 
starch  eaten.  Ptyalin  has  no  action  on  the  disaccharides  or 
monosaccharides,  nor  does  the  gastric  juice  so  far  as  is  known 
contain  any  enzyme  which  can  attack  these  sugars.  Sucrose 
may  be  partially  hydrolyzed  in  the  stomach,  but  this  effect 
appears  to  be  produced  by  the  free  hydrochloric  acid  of  the 
gastric  juice  and  not  by  an  enzyme.  These  statements,  of 
course,  refer  only  to  the  digestive  ferments,  and  not  to  the 
bacteria  which  may  be  present  in  the  stomach  and  may 
attack  the  sugars. 

On  reaching  the  small  intestine  the  starch  and  dextrin  are 
attacked  by  the  pancreatic  amylase  (amylopsin)  and  hydro- 
lyzed to  maltose.  At  the  same  time  that  it  is  undergoing 
pancreatic  digestion  the  food  mass  is  exposed  to  the  action  of 

84 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   85 

the  intestinal  juice,  which  contains  specific  ferments  having 
the  property  of  hydrolyzing  the  disaccharides  into  monosac- 
charides. Maltose,  as  already  explained,  yields  2  molecules 
of  glucose ;  cane  sugar,  i  molecule  each  of  glucose  and  fruc- 
tose (levulose) ;  and  milk  sugar,  a  molecule  each  of  glucose 
and  galactose.  It  is  possible  that  the  splitting  of  the  lac- 
tose (milk  sugar)  may  occur  in  the  intestinal  wall  rather 
than  in  the  food  mass. 

The  bulk  of  the  carbohydrate  of  the  food,  having  been  con- 
verted into  monosaccharides  in  the  intestine,  is  taken  up  by 
the  capillary  blood  vessels  of  the  intestinal  wall  and  passes 
from  them  into  the  portal  vein.  After  a  meal  rich  in  carbo- 
hydrate the  blood  of  the  portal  vein  is  rich  in  glucose  (some- 
times reaching  twice  its  normal  glucose  content)  and  may 
show  levulose  and  galactose  as  well  as  glucose.  In  the  blood 
of  the  general  circulation,  however,  only  glucose  is  found, 
•and  this  remains  small  in  quantity  —  about  one  tenth  of  one 
per  cent  —  even  after  a  meal  rich  in  carbohydrates,  so  that  a 
considerable  part  of  the  carbohydrate  taken  must  be  stored 
temporarily  in  the  liver  and  given  up  gradually  to  the  blood 
in  the  form  of  glucose,  thus  keeping  nearly  constant  the  glu- 
cose content  of  the  blood  of  the  general  circulation.  The  car- 
bohydrate thus  stored  in  the  liver  cells  is  deposited  in  the 
form  of  glycogen,  which,  after  an  abundant  meal,  may  reach 
10  per  cent  of  the  weight  of  the  liver  (or,  in  rare  cases,  an  even 
higher  figure)  and  may  fall  to  nearly  nothing  when  no  carbo- 
hydrate food  has  been  taken  for  some  time.     To  a  less  extent 


86  CHEMISTRY    OF    FOOD    AND    NUTRITION 

the  muscles  store  glycogen  in  a  similar  way,  their  glycogen 
contents  varying  from  traces  to  about  2  per  cent. 

However,  the  fact  that  the  carbohydrate  stored  in  the 
liver  after  a  meal  is  usually  converted  into  glucose  and  passes 
into  the  blood  current  before  the  next  meal,  while  the  glu- 
cose content  of  the  blood  remains  small  and  nearly  constant, 
indicates  that  the  glucose  of  the  blood  must  be  quite  rapidly 
used,  and  from  our  present  standpoint  the  most  important 
question  of  the  carbohydrate  metabolism  is  the  fate  of  the 
glucose  carried  to  the  tissues  by  the  blood. 

Of  the  glucose  which  the  blood  carries  away  from  the 
liver,  the  greater  part  disappears  in  the  muscles.  It  has 
often  been  showTi  by  comparison  of  the  arterial  with  the 
venous  blood  that  in  its  passage  through  the  muscles  the 
blood  becomes  poorer  in  glucose  and  oxygen  and  richer  in 
carbon  dioxide,  and  that  this  change  is  greater  when  the 
muscle  is  active  than  when  it  is  at  rest.  It  is  not  likely  that 
the  glucose  is  burned  in  the  muscle  directly  to  carbon  dioxide 
and  water;  a  certain  amount  of  lactic  acid  is  always  pro- 
duced by  working  muscle,  and  this  has  long  been  regarded 
as  an  intermediate  product  of  the  breaking  down  of  the 
glucose.  A  few  years  ago  it  was  rather  commonly  held 
that  the  glucose  brought  to  the  tissues  by  the  blood  became 
an  actual  part  of  the  living  cell  substance  before  being  oxi- 
dized. It  is  now  more  generally  believed  to  be  broken  down 
by  enzymes  acting  within  the  cells  (intracellular  enzymes) 
and  that  these  enzymes  are  influenced  in  their  action  by  an 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   87 

internal  secretion  of  the  pancreas,  since  removal  of  the 
pancreas  results  in  the  escape  of  glucose  through  the  kidneys 
as  in  diabetes.  Cohnheim  states  that,  while  the  juices 
obtained  by  pressure  from  muscles  and  from  pancreas  have 
little  effect  upon  glucose  when  tested  separately,  yet  when 
they  are  combined  and  glucose  added  they  cause  a  marked 
disappearance  of  the  glucose.  The  inference  from  this 
result  is  that  the  pancreas  furnishes  a  substance  which 
"activates"  the  glycolytic  enzyme  or  enzymes  of  the  muscles 
and  thus  makes  possible  the  normal  consumption  of  glucose 
in  the  body.  Since  pancreas  extracts  do  not  lose  this  prop- 
erty upon  boiling,  it  is  evident  that  the  activating  sub- 
stance is  not  an  enzyme,  but  some  more  stable  compound. 

At  least  two  kinds  of  enzymes  are  believed  to  be  involved 
in  the  consumption  of  glucose  in  the  tissue  cells :  (i)  cleavage 
enzymes,  which  split  the  molecule  into  fragments  more  easily 
oxidized;  and  (2)  oxidizing  enzymes,  or  oxidases,  which 
stimulate  the  oxidation  of  the  cleavage  products.  Both 
kinds  of  enzymes  are  widely  distributed  through  the  body 
and  are  beheved  to  be  normal  constituents  of  all  the  active 
cells.  Whatever  the  exact  mechanism  of  the  process,  a  large 
part  of  the  glucose  brought  by  the  blood  is  oxidized  in  the 
muscles  to  furnish  energy,  which  appears  as  external  or  in- 
ternal work. 

In  general,  the  rate  at  which  combustion  takes  place  in 
the  tissues  depends  upon  the  activity  of  the  tissue  cells, 
rather  than  upon  the  supply  either  of  combustible  matter 


bb  CHEMISTRY    OF    FOOD    AND    NUTRITION 

or  of  oxygen.  When  a  sufficient  supply  of  oxygen  is  provided, 
any  further  increase  has  little  effect  upon  the  rate  of  com- 
bustion, and,  as  we  have  seen,  any  excess  of  carbohydrate 
instead  of  being  burned  is  stored  as  glycogen.  But  while 
the  absorption  of  an  abundance  of  carbohydrate  does  not 
greatly  change  the  amount  of  combustion  taking  place  in 
the  body,  it  may  result  in  the  use  of  carbohydrate  as  fuel 
almost  to  the  exclusion  of  fat  for  the  time  being,  as  is  shown 
by  observations  upon  the  respiratory  quotient. 

The  respiratory  quotient  is  the  quotient  obtained  by 
dividing  the  volume  of  carbon  dioxide  given  off  in  respira- 
tion by  the  volume  of  oxygen  consumed.     That  is  — 

Volume  of  COo  produced       ^^  .  .        „ 

—  =     Respiratory  quotient. 

Volume  of  O2  consumed 

The  numerical  value  of  this  quotient  will  evidently  de- 
pend upon  the  elementary  composition  of  the  materials 
burned.  Carbohydrates  will  yield  a  quotient  of  i.o,  since 
they  contain  hydrogen  and  oxygen  in  proportions  to  form 
water,  so  that  all  oxygen  used  to  burn  carbohydrate  goes 
to  the  making  of  carbon  dioxide,  and  each  molecule  of  O2 
so  consumed  will  yield  one  molecule  of  CO2,  occupying  (under 
the  same  conditions  of  temperature  and  pressure)  the  same 
amount  of  space  as  the  oxygen  consumed  to  produce  it. 
Thus  in  burning  a  molecule  of  glucose,  six  molecules  of 
oxygen  are  consumed  and  six  molecules  of  carbon  dioxide 

produced :  — 

C6H12O6  +  6  O2  =  6  CO2  +  6  H2O. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   89 

Here  the  volumes  of  oxygen  and  of  carbon  dioxide  are  equal 
and  the  respiratory  quotient  is  i.o. 

Fats  contain  much  more  hydrogen  than  can  be  oxidized 
by  the  oxygen  present  in  the  molecule,  and  therefore  a  part 
of  the  oxygen  used  to  burn  fat  goes  to  form  water,  so  that  the 
volume  of  oxygen  consumed  is  considerably  greater  than  the 
volume  of  carbon  dioxide  produced,  which  gives  a  respiratory 
quotient  lower  than  i.o.  The  common  fats  of  the  body  and 
of  the  food  give  quotients  approximating  0.7.  Thus  the  oxi- 
dation of  stearin  is  represented  by  the  equation :  — 

2  CsvHnoOe  +  163  O2  =  114  CO2  +  no  H2O. 

Since  163  volumes  of  oxygen  are  consumed  and  114  volumes 
of  carbon  dioxide  produced,  the  respiratory  quotient  is 

-—  =  0.699. 
163 

Proteins  give  quotients  intermediate  between  those  of 
carbohydrates  and  fats,  but  if  the  amount  of  protein  used 
in  the  body  be  determined  by  other  methods  (see  Chapter 
VII)  and  allowed  for,  one  may  then  deduce  from  the  respira- 
tory quotient  the  proportions  of  carbohydrates  and  fats 
which  are  being  burned  in  the  body  at  any  given  time. 
The  body  will  show  a  respiratory  quotient  of  1.0  when  burn- 
ing carbohydrate  alone;  of  0.7  when  burning  fat  alone; 
and  of  an  intermediate  value  when  both  fat  and  carbohy- 
drate are  being  burned.  If,  now,  the  respiratory  quotient 
rises  soon  after  the  eating  of  carbohydrate  food,  it  can  only 


90  CHEMISTRY   OF   FOOD   AND   NUTRITION 

JDoean  that  the  carbohydrate  ii§  iKing  used  more  freely  and 
fat  less  freely  than  before..;  .r  [,;., 

b^^iiftn  jeixp^rini^nti  by;  Magnus-Levy  the  subject  before 
taking  iood  showed  a  quotient  of  0.77.  He  then  ate  155 
grams  of  cane  sugar,  after  which  the  quotient  was  determined 
at  intervals  of  an  hour  for  7  hours  with  the  following  results: 
ivoi,  0.89,  0.89,  0.92,  0.82,  0.82,  0.79.  The  quotient  here 
shows  that  within  an  hour  after  the  sugar  was  eaten  the  body 
-^s m^kwgluse-of  the  carbohydrate  to  such  an  exte;nt  that 
fat  either-^^^  Hot  being  used  at  all  or  was  being  formed  from 
carbohydra^te  as  fast^^  it  was'' burned;  aadthat  for  seven 
hours  after  the  meal  the  body  continued  to  use  carbohydrate 

to  a  greater,  and  fat  to  a  less,  extent  than  was  the  case  at 

,r  1  .  .  VUii-'  ■  •  .bo'julA'jin  'jlAzoib  nod:.  ■  10 
the  beginning  of  the  experiment. 

It  has  been  pointed  out  that,  when  carbohydrate  is  ab- 
sorbed in  larger  quantity  than  is  required  to  meet  the  body's 
immediate  needs  for  fuel,  the  surplus  normally  accumulates 
as  glycogen,  which  is  stored  conspicuously  in  the  liver,  but 
also  to  a  considerable  extent  in  the  muscles  and  other  organs. 
The  amount  of  carbohydrate  which  will  be  stored  in  the 
entire  body  after  rest  and  hberal  feeding  is  estimated  at 
300-400  grams,^  of  which  the  liver  will  probably  contain 
about  one  half. 

Production  oj  Fat  from  Carbohydrate.  —  When  the  supply 
of  carbohydrate  is  so  abundant  that  it  continues  in  excess 

^  Thus  the  total  amount  of  carbohydrate  which  can  be  stored  as  such 
in  the  body  is  no  more  than.is  frequently  taken  in  one  day's 4oodi  cObi'i 


THE   FATE    OF    THE   FOODSTUFFS   IN   METABOLISM      Qfi 

of  the  needs  of  the  body  and  accuniulates  until  the  liver  and 
muscles  have  no  tendency  to  increase  their  store  of  glycogen, 
the  further  surplus  of  carbohydrate  ttodls  ;to  be  converted 
into  fat.  jiaoooSl 

Although  the  readiness  with  which  some  farm '  animals 
are  fattened  on  essentially  carbohydrate  food  would  seem 
to  have  been  sufficient  to  convince  early  observers  of  the  transi 
formation  of  carbohydrate  into  fat  in  the  body,  thisf;  evin 
dence  appears  to  have  been  overlooked  because  of  the  idqa> 
for  a  long  time  prevalent,  that  simpler  substances  are  built 
up  into  more  complex  compounds  only  in  the  plant,  and  not 
in  the  animal  organism.  In  recent  years  it  has  become 
necessary  to  abandon  this  latter  assumption  completely, 
and  there  is  now  abundant  evidence  that  the  animal  body 
synthesizes  fat  from  carbohydrate. 

The  most  obvious  method  of  demonstrating  the  conver- 
sion of  carbohydrate  into  fat  is  that  followed  by  Lawes  and 
Gilbert.  Several  pigs  of  the  same  litter  and  of  similar  size 
were  selected;  some  were  killed  and  analyzed  as  "controls," 
while  the  others  were  fed  on  known  rations  and  later  weighed, 
killed,  and  analyzed  to  determine  the  kinds  and  amounts 
of  material  stored  in  the  body.  In  several  cases  the  amounts 
of  fat  stored  during  such  feeding  trials  were  found  to  have 
been  much  larger  than  could  be  accounted  for  by  all  of  the 
fat  and  protein  fed,  so  that  at  least  a  part,  and  in  some  cases 
the  greater  part,  of  the  body  fat  must  have  been  formed  from 
the  carbohydrate  of  the  food.     Many  similar  experiments 


92  CHEMISTRY    OF   FOOD   AND   NUTRITION 

have  been  made,  and  the  transformation  of  carbohydrate 
into  fat  has  been  demonstrated  by  this  method  in  carniv- 
orous as  well  as  herbivorous  animals. 

Recently  it  has  also  been  shown  that  carbohydrates  con- 
tribute to  the  production  of  milk  fat.  Jordan  and  Jenter 
kept  a  milch  cow  for  fifty-nine  days  upon  food  from  which 
nearly  all  of  the  fat  had  been  extracted.  During  this  period 
about  twice  as  much  milk  fat  was  produced  as  could  be  ac- 
counted for  by  the  total  fat  and  protein  of  the  food,  and 
in  addition  the  cow  gained  in  weight  and  her  appearance 
showed  that  she  had  more  body  fat  at  the  end  than  at  the 
beginning  of  the  experiment. 

Instead  of  determining  directly  the  fat  formed  in  the 
animal  fed  on  carbohydrate,  the  production  of  fat  from  car- 
bohydrate may  be  demonstrated  by  keeping  the  animal 
experimented  upon  in  a  respiration  chamber  so  arranged 
that  the  total  carbon  given  oflF  from  the  body  may  be  deter- 
mined and  compared  with  the  total  carbon  of  the  food. 
If  in  such  a  case  the  body  is  found  to  store  more  carbon  than 
it  could  store  as  carbohydrate  or  protein,  it  is  safe  to  infer 
that  at  least  the  excess  of  stored  carbon  is  held  in  the  form 
of  fat.  Many  such  experiments  upon  dogs,  geese,  and  svdne 
have  shown  storage  of  carbon  very  much  greater  than  could 
be  accounted  for  on  any  other  assumption  than  that  a  part 
of  the  carbon  of  the  carbohydrates  eaten  remained  in  the 
body  in  the  form  of  fat. 

Further  e\'idence  of  the  transformation  of  carbohydrate 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   93 

into  fat  is  obtained  from  the  respiratory  quotient.  As  noted 
above,  observations  made  after  a  fast  tend  to  show,  quotients 
approaching  that  of  fat,  while  after  feeding  carbohydrates 
the  quotient  may  rise  rapidly.  If  the  quotient  reaches  i.o, 
it  shows  that  the  body  as  a  whole  is  using  carbohydrate  and 
not  fat  as  fuel;  and  a  quotient  greater  than  i.o  can  only  mean 
that  the  carbohydrate  is  itself  supplying  part  of  the  oxygen, 
which  appears  as  carbon  dioxide,  or,  in  other  words,  that  it 
is  breaking  down  in  such  a  way  that  a  part  is  burned  while 
another  part  goes  to  form  in  the  body  a  substance  more 
highly  carbonaceous  and  having  a  lower  respiratory  quotient 
than  the  carbohydrate  itself.  In  many  cases  it  is  certain 
that  this  substance  can  be  nothing  but  fat.  Respiratory 
quotients  greater  than  1.0  have  been  observed  after  liberal 
carbohydrate  feeding  in  many  animals,  including  men. 
Each  such  observation  furnishes  evidence  of  a  conversion 
of  carbohydrate  into  fat. 

The  formation  of  fat  from  carbohydrate  in  the  animal 
body  is  therefore  estabhshed  by  four  distinct  lines  of  ex- 
perimental evidence:  (i)  by  determination  of  the  amounts 
of  body  fat  formed,  (2)  by  determination  of  the  milk  fat 
produced,  (3)  by  observation  of  the  amount  of  carbon  stored, 
(4)  by  observations  upon  the  respiratory  quotient. 

FAT 

The  gastric  juice  contains  a  fat-splitting  enzyme;  but  if 
the  fat  is  swallowed  in  any  other  than  a  finely  emulsified 


94  CHEMISTRY   OF   FOOD   AND   NUTRITION 

state,  it  is  but  little  changed  in  the  stomach.  Emulsified 
fat  may,  however,  be  quite  largely  digested  by  the  gastric 
juice.  Volhard  found  78  per  cent  of  th^  fat  of  egg  yolk  to 
be  digested  into  fatty  acids  and  glycerol  in  the  stomach. 
The  gastric  juice  also  digests  a  large  part  of  the  fat  of  milk, 
and  it  is  probably  through  the  action  of  the  gastric  Upase 
that  infants  are  able  to  digest  relatively  large  amoimts  of 
milk  fat  before  the  pancreatic  juice  becomes  active.  Fat  is 
spUt  by  the  digestive  lipases  into  glycerol  and  fatty  acid, 
of  which  the  former  is  readily  soluble  in  water,  and  the  latter 
is  soluble  in  bile,  so  that  it  may  be  said  that  in  intestinal 
digestion  the  fat  is  split  to  soluble  products  and  probably 
absorbed  in  solution. 

Whether  the  sphtting  of  all  fat  into  fatty  acid  and  glycerol 
is  absolutely  essential  to  its  absorption  is  still  undecided; 
but  recent  work  indicates  that,  as  a  rule  at  least,  the  fat  eaten 
is  thus  hydrolyzed  in  the  stomach  or  intestine  and  is  ab- 
sorbed as  fatty  acid  and  glycerol  which  recombine  in  their 
passage  through  the  intestinal  wall.  Very  Ukely  this  re- 
combination is  also  stimulated  by  Upases,  since  these  enzymes 
show  to  a  marked  degree  the  property  of  being  able  to  accel- 
erate a  reaction  in  either  direction  according  to  circumstances 
(''reversible  action  of  enzymes").  The  fat  thus  absorbed 
is  taken  up  by  the  lymph  vessels  rather  than  the  capillary 
blood  vessels,  and  is  poured  with  the  lymph  into  the  blood, 
so  that  the  blood  plasma  may  become  turbid  or  even  milky 
after  a  meal  rich  in  fat.    In  the  blood  the  neutral  fat  appears 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   95 

to  be  changed  into  an  unknown,  soluble,  dialyzable  modi- 
fication and  passes  in  this  state  through  the  capillary  walls 
into  the  tissues,  where  it  reverts  to  ordinary  insoluble  fat 
and  can  be  seen  as  microscopic  droplets  or  larger  masses 
lying  in  the  cell.  In  this  way  the  fat  which  renders  .the 
blood  plasma  turbid  at  the  height  of  absorption  will  usually 
have  disappeared  after  a  few  hours,  having  been  partly  de- 
posited in  various  organs,  and  partly  burned  as  fuel.  The 
fat  thus  burned  as  fuel  is  for  the  most  part  utilized  by  the 
tissues  for  the  production  of  energy.  In  experiments 
with  isolated  working  muscles,  it  is  not  so  easy  to  show 
the  direct  utilization  of  the  fat,  as  of  the  carbohydrate, 
and  so  Chaveau  and  some  other  physiologists  have  held 
that  fat  is  not  used  by  the  muscles  directly,  but  is  first 
broken  down  (probably  in  the  liver)  with  the  formation  of 
glucose,  and  that  the  latter  is  then  carried  to  the  muscles 
and  used  by  them  as  already  described.  That  the  liver 
cells  can  use  fat  as  well  as  glycogen  and  protein  for  the 
manufacture  of  glucose  to  keep  up  the  normal  composition 
of  the  blood  is  probably  true,  but  it  is  not  true  (as  was  thought 
by  Chaveau)  that  the  value  of  fat  as  a  source  of  energy  for 
muscular  work  is  only  proportional  to  the  dextrose  which 
could  be  obtained  from  it  according  to  the  reaction:  — 

2  CgyHnoOe  +  67  O2  =  16  CeHisOe  +  18  CO2  +  14  H2O, 

which  would  involve  a  loss  hi  about  one  third  of  the  fuel 
value  of  the  fat.     The  average  results  of  a  very  complete 


96  CHEMISTRY    OF   FOOD    AND    NUTRITION 

series  of  experiments  by  Atwater  and  his  associates  indicated 
that  the  potential  energy  of  fat  was  95.5  per  cent  as  efficient 
as  that  of  carbohydrates  for  the  production  of  muscular 
work. 

In  discussing  the  formation  of  body  fat  from  carbohydrate 
it  was  shown  that  often  the  greater  part  of  the  fat  stored  is 
manufactured  in  the  body  from  carbohydrate.  So  striking 
were  the  results  of  some  of  the  experiments  demonstrating 
the  synthesis  of  fat  from  carbohydrate,  that  physiologists 
came  to  question  for  a  time  whether  any  of  the  fat  deposited 
in  the  tissues  comes  directly  from  the  food.  Abundant  evi- 
dence that  food  fats  may  be  directly  deposited  in  the  body 
has  been  obtained  by  feeding  characteristic  fats  to  dogs  and 
showing  that  these  fats  can  afterwards  be  recognized  in  the 
tissues  of  the  animals.  Experiments  of  this  kind  have  been 
made,  using  linseed  oil,  rapeseed  oil,  or  mutton  tallow,  any 
of  which  is  easily  distinguishable  by  its  chemical  and  physical 
properties  from  the  fat  normally  found  in  the  body  of  the  dog. 
Munk  starved  a  dog  for  19  days,  and  then  for  14  days  fed  a 
mixture  of  the  fatty  acids  obtained  from  mutton  tallow,  as  a 
consequence  of  which  about  one  half  of  the  weight  lost  by 
fasting  was  regained.  The  dog  was  then  killed  and  yielded 
on  dissection  iioo  grams  of  fat  melting  at  40°,  which  is  about 
the  melting  point  of  mutton  tallow,  whereas  normal  dog  fat 
melts  at  about  20°.  In  another  experiment  by  Munk  rape 
oil  was  fed  and  the  fat  obtained  from  the  dog  was  found  to 
contain  82.4  per  cent  of  oleic  and  erucic  acids  and  12.3  per 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   97 

cent  of  solid  acids,  whereas  normal  dog  fat  had  only  65.8  per 
cent  oleic,  no  erucic,  and  28.8  per  cent  of  solid  fatty  acids. 

The  occurrence  in  the  body  fat  of  properties  usually  char- 
acteristic of  some  particular  fat  which  has  been  fed  is  now 
very  well  known  and  is  recognized  in  establishing  standards 
of  purity  for  fats  of  animal  origin.  Thus,  the  lard  obtained 
from  swine  which  have  been  fed  cottonseed  meal  shows 
the  characteristic  color  reactions  of  cottonseed  oil,  and  more 
elaborate  tests  must  be  made  in  order  to  determine  whether 
cottonseed  fat  has  actually  been  mixed  with  the  lard. 

European  food  officials  sought  to  establish  an  easy  method 
of  distinguishing  between  butter  and  its  substitutes  by  re- 
quiring manufacturers  of  any  butter  substitute  to  use  a  cer- 
tain proportion  of  sesame  oil  in  the  preparation,  sesame  oil 
having  a  characteristic  color  reaction  which  can  be  very 
easily  demonstrated  without  the  use  of  laboratory  facilities. 
It  was  found,  however,  that  the  same  sesame  oil  reaction 
might  be  exhibited  by  a  perfectly  pure  butter  fat  from  cows 
which  had  been  fed  upon  sesame  meal. 

Evidence  of  the  formation  of  body  fat  from  food  fat  has 
also  been  obtained  by  experiments  upon  the  total  amount 
of  fat  formed  in  the  body  when  the  amount  and  composition 
of  the  food  eaten  was  accurately  known.  Hoffmann  starved 
a  dog  until  its  weight  had  decreased  from  26  to  16  kilograms, 
so  that  it  must  have  been  almost  devoid  of  fat.  He  then 
fed  small  amounts  of  meat  and  large  amounts  of  fat  for  five 
days,  after  which  the  dog  was  killed  and  analyzed.     The 


98  CHEMISTRY    OF   FOOD   AND   NUTRITION 

body  contained  1353  grams  of  fat,  of  which  not  over  131 
grams  could  have  come  from  proteins,  and  only  a  few  grams 
at  most  from  the  small  amount  of  carbohydrates  in  the 
meat  fed,  so  that  about  nine  tenths  of  the  fat  which  the 
animal  had  laid  on  must  have  come  from  the  fat  of  the  food. 
Whether  fat  once  deposited  in  the  tissues  will  remain  and 
accumulate  or  be  returned  to  the  circulation  and  used  as 
fuel,  will  depend  upon  the  balance  between  the  food  con- 
sumption and  the  food  requirements  of  the  organism  as  a 
whole.  In  this  respect,  there  is  no  difference  between  fat 
consumied  and  deposited  as  such  and  fat  formed  in  the 
body  from  other  food  materials. 

Formation  oj  Carbohydrate  from  Fat.  —  That  fat  which 
has  been  deposited  in  the  body  can  be  drawn  upon  for  the 
production  of  carbohydrate  would  appear  probable  from 
the  fact  that  hibernating  animals  seem  to  use  their  stored  fat 
to  maintain  the  constant  glucose  content  of  the  blood.  In 
addition  to  this,  experiments  are  on  record  in  which  the 
actual  amount  of  glycogen  in  the  body  has  been  found  to  in- 
crease (apparently  at  the  expense  of  the  body  fat)  during 
the  period  of  hibernation  (Hill). 

The  formation  of  carbohydrate  from  fat  appears  also  to 
have  been  shown  by  observations  in  which  the  respiratory 
quotient  has  been  found  to  be  less  than  0.7  at  times  when 
the  body  was  knowTi  to  be  using  up  considerable  quantities 
of  fat.  Since  it  is  not  conceivable  that  any  large  amount 
of  material  having  a  respiratory  quotient  materially  less  than 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   99 

o.  7  can  have  been  directly  available  for  combustion  in  the  body, 
this  low  quotient  appears  to  be  due  to  the  fact  that  fat  may 
be  broken  down  in  such  a  way  as  to  be  transformed  in  part 
into  carbohydrate  (respiratory  quotient  i),  the  remainder 
of  the  fat  molecule  undergoing  oxidation  and  giving  for  the 
time  being  the  unusually  low  respiratory  quotient.  It  will 
be  seen;  that  this  is  evidence  of  exactly  the  same  kind  as  was 
cited  in  discussing  the  formation  of  fat  from  carbohydrates 
in  the  body.  Since  carbohydrate  has  a  respiratory  quotient 
of  I,  fat  of  0.7,  and  protein  an  intermediate  respiratory  quo- 
tient, and  since  the  protein  metabolism  can  be  estimated  by 
other  methods  andiftUowed'  for,  it  is  evident  that  a  quotient 
greater  than  i  will;  indicate  a  transformation  of  carbohydrate 
into  fat,  and  a  quotient  less  than  0.7  similarly  indicates  a 
transformation  of  fat  into  carbohydrate. 

In  phloridzin  poisoning,  however,,  where  there  is  abundant 
evidence  of  the  formation  of .  gluiCGse  frpm  protein,  there  is 
not  equally  strong  evidenciei of  itis  formation  ;from  fat;  and 
some  physiologists  doubt  r!the;;^J:)ility  .of  itjie  anijnal  body  to 
form  carbohydrate  from  fat;  beyond ,  what  •  can  be  derived 
from  the  glyceryl  radicle,:  and  explain  the  respiratory  quor 
tient  of  less  than  0,7  j  as :  due  to  a  storage  pf  oxygen,  Stay,- 
ling,  on  the  oth^r  hand,  is.,oi3the  opinion  that  /Hh^re  risi  jQQ  (evi- 
dence that  the  body  in  an3ri<?f|its 'tissjyi^s  i§r  able  tp;  &toi:f ;  o^yr 
^n j  V!  f  and  <  that  l  jwhile ;  mahy  physiologists  [  mgH', ,  npt  agree 
,with  this  statement,  all  would  agree  that  the  ppwctr  of, living 
tissues  to ;Stpre,  oxygen  is  extremely  ltmifcedfiio»  ji  io  J^oni 


lOO  CHEMISTRY    OF   FOOD    AND    NUTRITION 

It  is  well  known  that  many  plants  lay  up  a  store  of  food 
in  the  seeds  in  the  form  of  fat  and  that  on  germination  this 
fat  is  transformed  into  carbohydrate  and  carried  as  carbo- 
hydrate to  the  growing  parts  of  the  young  plant. 

The  greater  part  of  the  evidence  appears  to  favor  the  view 
that  animals  as  well  as  plants  can  change  fat  into  carbohy- 
drate, but  this  is  by  no  means  so  conclusively  demonstrated 
as  the  formation  of  fat  from  carbohydrate  or  of  carbohydrate 
from  protein. 

PROTEINS 

So  long  as  the  swallowed  food  remains  in  an  alkaline  or 
neutral  condition  in  the  stomach,  and  until  it  becomes  mixed 
with  gastric  juice,  the  proteins  are  unchanged.  Little  by 
little,  as  described  above  (Chapter  III),  the  food  becomes 
mixed  with  the  gastric  juice,  which,  as  secreted  in  the  middle 
portion  of  the  stomach  under  normal  conditions,  always  con- 
tains free  hydrochloric  acid.  This  free  acid  acts  upon  the 
proteins  of  the  food,  converting  them  into  the  meta-protein 
acid-albumin  ("syntonin"),  which  in  turn  under  the  influ- 
ence of  pepsin  spUts  down  wdth  the  formation  of  proteoses, 
and  these  by  further  hydrolysis  yield  peptones. 

Ordinarily  the  food  mass  is  passed  from  the  stomach  into 
the  intestine  before  the  digestion  of  protein  has  gone  very 
far.  In  artificial  digestion  experiments  with  pepsin  ordina- 
rily only  a  part  of  the  protein  is  split  to  the  form  of  peptone, 
most  of  it  going  no  farther  than  the  proteose  stage.     More- 


THE   TATE    OF    THE    FOODSTUFFS    IN    METABOLISM       lOI 

over,  gastric  digestion  of  proteins  is  not  strictly  essential, 
for  it  has  been  found  by  experiments  on  animals,  and  obser- 
vations upon  men,  that  digestion  of  proteins  takes  place  after 
complete  removal  of  the  stomach.  The  stomach  digestion 
of  proteins  is  thus  less  important  than  was  formerly  sup- 
posed, but  probably  facilitates  their  more  extensive  digestion 
in  the  intestine. 

On  reaching  the  small  intestine  the  proteins  are  attacked 
by  trypsin,  the  proteolytic  enzyme  of  the  pancreatic  juice. 
Trypsin  works  best  in  an  alkaline,  but  can  work  in  a  neutral 
or  slightly  acid,  medium.  Its  activity  is  retarded,  but  it  is 
not  destroyed,  by  small  amounts  of  hydrochloric  acid,  hence 
the  entrance  of  the  acid  stomach  contents  into  the  intestine 
can  do  no  more  than  temporarily  check  tryptic  digestion. 
Generally  speaking,  the  conditions  are  favorable  to  the  ac- 
tion of  tr)^sin  throughout  the  whole  length  of  the  small 
intestine,  and  its  action  is  supplemented  by  that  of  the  erepsin 
of  the  intestinal  juice.  The  action  of  trypsin  on  protein  is 
first  to  form  proteoses.  These  are  then  hydrolyzed  to  pep- 
tones, which  are  in  turn  split  down  by  the  continued  action  of 
the  trypsin,  but  more  particularly  by  erepsin,  with  the  for- 
mation of  amino  acids.  Different  views  are  held  as  to  how 
far  the  splitting  of  protein  actually  goes  in  normal  digestion. 
Some  believe  that  it  is  entirely  spht  to  amino  acids,  especially 
since  the  enzyme  erepsin  has  been  shown  to  be  a  normal  con- 
stituent of  the  intestinal  juice  and  to  have  the  specific  func- 
tion of  splitting  proteoses  and  >peptones  to  amino  i^^ids  and 


I02  CHEMISTRY    OF    FOOD    AND    NUTRITION 

ammonia.  An  objection  to  this  view  is  that  it  requires  the 
assumption  that  all  the  protein  in  the  body  has  been  synthe- 
sized (either  during  or  after  absorption)  from  simple  amino 
acids,  which  would  therefore  appear  to  have  an  equal  nutri- 
tive value  with  the  proteins  themselves,  a  conclusion  as  yet 
hardly  satisfactorily  supported  by  feeding  experiments.  The 
results  of  feeding  experiments  with  the  products  of  hydrolytic 
cleavage  of  proteins  are  somewhat  conflicting,  but  according 
to  the  data  at  present  available  it  appears  to  be  possible  to 
support  the  protein  metaboHsm  of  dogs  with  the  products  of 
pancreatic  digestion  (carried  to  the  point  of  disappearance 
of  the  biuret  reaction),  but  not  with  the  products  of  acid  hy- 
drolysis. Abderhalden,  one  of  the  most  active  investigators 
in  this  field,  holds  that  while  a  large  amount  of  amino  acid 
is  formed  in  normal  digestion,  there  always  remains  and  is 
absorbed  a  polypeptid  nucleus  which  serves  as  a  starting  point 
for  the  rebuilding  of  proteins  in  the  body.  According  to 
Abderhalden 's  view,  the  digestion  of  protein  might  be  repre- 
sented as  follows :  — 

Native  protein 

I 

Meta-protein 
Proteoses 

I 

Peptones 


Polypeptid  Amino  acids 

Abderhalden  says:  "It  is  at  present  uncertain  as  to  how 
far  the.^sijitegration  goes-in  individual  cases,  as  to  whether 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   103 

polypeptids  with  a  small  number  of  amino  acids  result,  or 
that  the  digestion  stops  while  the  chains  are  more  complicated. 
.  .  .  We  can  draw  no  conclusion  as  to  the  extent  of  the  de- 
composition simply  on  account  of  the  appearance  of  free 
amino  acids.  More  complex  substances  may  be  present  at 
the  same  time." 

Henriques/  however,  holds  that  a  mixture  of  amino  acids 
without  polypeptids  may  suffice  to  maintain  the  animal  or- 
ganism in  nitrogen  equilibrium. 

The  digestion  products  of  the  proteins  pass  on  by  absorption 
mainly  into  the  capillary  blood  vessels  and  thence  to  the 
portal  vein.  It  was  formerly  stated  that  either  in  passing 
through  the  intestinal  epithelium,  or  perhaps  under  the  in- 
fluence of  the  blood,  the  digestion  products  are  changed  to 
serum  albumin  and  serum  globulin.  While  such  a  statement 
must  not  be  accepted  too  literally  or  regarded  as  a  complete 
explanation  of  what  occurs,  it  is  still  commonly  held  that  the 
first  proteins  built  in  the  body  from  the  digestion  products 
circulate  in  the  blood  and  finally  serve  as  a  basis  for  the  syn- 
thesis of  the  more  complex  protein  bodies  found  in  the  various 
tissues  and  secretions,  several  of  which  are  characteristic  of 
the  particular  organs  or  groups  of  cells  in  which  they  are  found. 
The  fact  that  Howell  has  recently  obtained  positive  reactions 
for  amino  acids  in  the  blood  emphasizes  the  importance  of 
these  compounds  in  metabolism  and  indicates  that  they  are 

1  Zeitschrift  f.  physiologische  Chemie,  1907,  54,  406  ;  Lusk,  Science  oj 
Nutrition,  2d  ed,,  p.  116. 


I04  CHEMISTRY    OF   FOOD    AND    NUTRITION 

not  entirely  synthesized  to  protein  immediately  upon  absorp- 
tion. 

Autolytic  enzymes,  capable  of  breaking  down  the  proteins 
of  the  body  tissues  and  fluids  with  production  of  amino  acids 
apparently  identical  with  those  formed  in  digestion,  are 
found  in  all  of  the  organs,  and  it  is  not  improbable  that  pro- 
tein synthesis  also  may  be  brought  about  by  every  living  cell. 
In  a  recent  discussion  of  the  subject,  Chittenden  says:  "We 
can  well  imagine  that  in  the  life  and  death  of  tissue  cells 
autolytic  decompositions  are  constantly  taking  place  whereby 
cell  protein  is  broken  down  into  its  component  parts,  while 
at  the  same  time  a  synthesis  of  protein  may  be  occurring 
from  other  amino  acids  brought  by  blood  or  lymph,  with  a 
possible  utilization  of  some  of  the  fragments  Uberated  by 
the  autolysis." 

Abderhalden  from  an  equally  advanced  viewpoint  sees  a 
new  indication  of  the  synthesis  of  body  proteins  in  the  intesti- 
nal wall,  in  experiments  in  which  horses  were  bled,  fasted, 
and  bled  again,  then  fed  with  gliadin,  a  protein  which  contains 
about  37  per  cent  of  glutamic  acid,  whereas  the  blood  pro- 
teins contain  only  about  8  per  cent.  The  amounts  of  glu- 
tamic acid  obtainable  from  the  blood  of  the  horses  remained 
very  constant  throughout,  in  spite  of  the  fact  that  the  horses 
while  supplied  only  TNith  gliadin  had  to  replace  the  protein 
material  removed  in  bleeding.  Abderhalden  therefore  con- 
siders that  "the  protein  of  the  food  must  certainly  have  under- 
gone a  complete  change  before  it  entered  into  the  circulation." 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   I05 

Whatever  the  mechanism  of  their  assimilation,  the  absorbed 
proteins  soon  become  available  for  the  nutrition  of  the  body, 
and  among  other  functions  they,  like  the  carbohydrates  and 
fats,  may  be  burned  as  fuel  for  muscular  work.  Pfliiger 
proved  that  protein  may  serve  as  a  source  of  muscular  energy 
by  feeding  a  dog  for  7  months  delusively  upon  meat  practi- 
cally free  from  fat  and  carbohydrate,  and  requiring  it  through- 
out the  experiment  to  do  considerable  amounts  of  work,  the 
energy  for  which  must  in  this  particular  case  have  been 
derived  largely  from  the  protein  consumed. 

Until  recently  it  was  generally  believed  that  a  large  part, 
if  not  the  greater  part,  of  the  protein  was  built  up  into  body 
material  of  some  sort  before  being  broken  down,  but  since 
protein  does  not  accumulate  in  the  grown  body,  except  under 
special  conditions,  it  is  evident  that  the  building  up,  or  ana- 
boHc  process,  if  it  occurs  so  extensively,  must  be  either  ac- 
companied or  immediately  followed  by  a  breaking  down,  or 
katabolism,  of  protein.  By  experiment  it  has  been  found  that 
if  a  meal  extra  rich  in  protein  be  eaten  an  increased  elimi- 
nation of  nitrogenous  end  products  can  be  observed  within 
2  or  3  hours,  and  probably  much  the  greater  part  of  the  surplus 
nitrogen  will  have  been  excreted  within  24  hours  of  the  time 
it  was  taken  into  the  stomach.  It  does  not  follow,  however, 
that  the  whole  of  the  protein  molecule  is  broken  down  and 
eliminated  so  quickly,  and  experiments  have  shown  that  the 
carbon  of  extra  protein  fed  does  not  leave  the  body  so  rapidly 
as  does  the  nitrogen.     Evidently,  the  nitrogenous  radicles  of 


I06  CHEMISTRY    OF   FOOD   AND    NUTRITION 

the  protein  may  be  split  off  in  such  a  way  as  to  leave  a  non- 
nitrogenous  residue  in  the  body,  and  the  study  of  protein 
metabolism  involves  a  consideration  of  the  fate  of  both  the 
nitrogenous  and  the  non-nitrogenous  derivatives.  The  fate 
of  the  latter  may  conveniently  be  considered  first  on  account 
of  its  relation  to  the  metabolism  of  carbohydrates  and  fats. 

It  can  be  readily  calculated  that  to  provide  for  the  elimina- 
tion of  aU  the  nitrogen  of  protein  in  the  form  of  the  usual 
end  products  would  require  much  the  smaller  part  of  the 
carbon,  hydrogen,  and  potential  energy  of  the  original  protein. 
WTiile  such  a  calculation  gives  no  picture  of  the  actual  mech- 
anism of  protein  kataboUsm,  it  suffices  to  show  the  quanti- 
tative significance  of  the  non-nitrogenous  residue  which  the 
protein  molecule  may  jdeld,  and  the  importance  of  determin- 
ing to  what  extent  this  residue  may  be  actually  transformed 
into  carbohydrate  or  fat  in  the  body. 

Formation  of  Carbohydrak  from  Protein.  —  As  early  as  1876 
Wolffberg  tested  the  formation  of  carbohydrate  from  protein 
by  fasting  fowls  for  two  days  in  order  to  free  them  from  glyco- 
gen and  then  feeding  for  two  days  with  meat  powder  which 
had  been  washed  free  from  carbohydrate.  Two  of  the  fowls 
were  killed  soon  after  this  protein  feeding  and  showed  more 
glycogen  in  their  Uvers  and  muscles  than  could  be  accounted 
for  except  as  derived  from  the  protein  fed.  Two  similar  fowls 
killed  17  and  24  hours  after  feeding  showed  much  less  glyco- 
gen. This  formation  of  glycogen  from  protein  was  fully  con- 
firmed by  Kulz  in  a  long  series  of  experiments  in  which  the 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   107 

food  consisted  of  chopped  meat  thoroughly  extracted  with 
warm  water  (Lusk). 

Independent  evidence  of  the  production  of  carbohydrates 
from  protein  is  found  in  the  work  of  Seegen,  who  chopped 
and  mixed  the  Uver  of  a  freshly  killed  animal  and  determined 
the  amount  of  carbohydrate  in  it  by  analysis  of  a  portion,  while 
the  remainder  was  kept  at  body  temperature  and  sampled  for 
analysis  from  time  to  time.  The  percentage  of  carbohydrate 
was  found  to  increase,  showing  that  the  liver  cells  can  form 
carbohydrate  from  their  own  protein  substance. 

The  most  striking  evidence  of  the  origin  of  carbohydrate 
from  protein  in  the  animal  body  is  found  in  the  many  observa- 
tions and  experiments  which  have  been  made  in  cases  of  dia- 
betes, and  in  experimental  glycosuria  produced  either  by 
administration  of  phloridzin  or  by  removal  of  the  pancreas. 
In  such  cases  large  amounts  of  carbohydrate  may  be  given  off 
in  the  form  of  glucose  even  when  there  is  little  body  fat  and 
no  carbohydrate  or  fat  is  fed.  The  glucose  must  therefore 
result  from  the  metabolism  of  protein.  In  Lusk's  exhaustive 
experiments  upon  dogs  rendered  diabetic  by  phloridzin,  58 
per  cent  of  the  total  weight  of  protein  broken  down  in  the 
body  (whether  in  fasting  or  on  a  meat  diet)  was  eliminated  in 
the  form  of  glucose.  According  to  Lusk :  "After  ingestion  of 
protein  in  the  normal  organism  this  sugar  becomes  early  avail- 
able and  inay  be  burned  before  the  nitrogen  belonging  to  it  is 
eliminated,  or,  if  the  sugar  be  formed  in  excess,  it  may  be 
stored  as  glycogen  in  the  liver  and  muscles  for  subsequent  use. 


Io8  CHEMISTRY    OF    FOOD    AND    NUTRITION 

In  this  way  it  is  obvious  that  at  least  half  the  energy  in  pro- 
tein may  be  independent  of  the  curve  of  nitrogen  elimination, 
but  may  rather  act  as  though  it  had  been  ingested  in  the 
form  of  carbohydrate."  While  Lusk's  conclusions  are  based 
mainly  upon  the  results  of  experiments  with  phloridzinized 
dogs,  there  seems  to  be  no  doubt  that  in  healthy  men  also  a 
large  part  of  the  protein  eaten  may  take  the  form  of  carbohy- 
drate in  the  course  of  its  metabolism  in  the  body. 

Recently  Lusk  has  experimentally  demonstrated  some  of 
the  ways  in  which  the  production  of  carbohydrate  from  pro- 
tein may  take  place.  Alanin,  one  of  the  prominent  cleavage 
products  of  protein,  yields  by  hydrolysis  lactic  acid  and  am- 
monia, and  the  lactic  acid  is  convertible  into  glucose.  In  the 
case  of  a  dog  which  had  been  sufficiently  treated  with  phlorid- 
zin  so  that  no  glucose  was  burned  in  the  body,  Lusk  recovered 
in  the  urine  an  amount  of  glucose  quantitatively  proportional 
to  the  amount  of  alanin  fed.  The  production  of  glucose  from 
glutamic  acid  has  also  been  studied  by  Lusk,  who  concludes 
that  this  acid  probably  yields  in  its  metabolism  a  molecule 
of  lactic  acid,  which  in  turn  may  be  converted  into  glucose. 

We  have  therefore  abundant  evidence  from  the  work  of 
independent  investigators,  using  different  methods,  that  the 
animal  body  may  form  carbohydrates  readily  and  in  large 
proportion  from  the  protein  of  the  food ;  and  the  mechanism 
of  the  process  is  beginning  to  be  fairly  well  understood. 

Production  of  Fat  from  Protein.  —  There  has  been  much  con- 
troversy regarding  the  formation  of  fat  from  protein  in  the 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   IO9 

animal  body.  A  number  of  observations  by  Voit  which  were 
believed  to  demonstrate  such  a  production  of  fat  have  since 
been  subjected  to  vigorous  criticism  by  Pfliiger  and  appar- 
ently shown  to  be  capable  of  other  interpretations.  New  ex- 
periments in  Voit's  laboratory  by  Cremer  appear,  however,  to 
establish  the  formation  of  body  fat  from  protein  food  beyond 
reasonable  doubt.  A  cat  after  a  preliminary  period  of  fasting 
was  placed  in  a  respiration  apparatus  and  fed  liberally  with 
lean  meat  for  eight  days.  The  amount  of  protein  broken 
down  in  the  body  was  estimated  from  the  nitrogen  eliminated. 
The  carbon  eliminated  was  also  measured,  and  it  was  found 
that  58.4  grams  of  carbon  had  been  retained  in  the  body. 
This  would  correspond  to  130  grams  of  glycogen,  but  the  total 
amount  of  glycogen  in  the  body  at  the  end  of  the  experiment 
was  only  35  grams,  hence  about  three  fourths  of  the  carbon 
retained  by  the  cat  from  the  protein  food  must  have  been 
stored  as  body  fat. 

The  evidence  of  formation  of  milk  fat  in  part  from  protein, 
while  perhaps  not  amounting  to  a  mathematical  demonstra- 
tion, is  still  very  strong. 

For  practical  purposes  the  outcome  of  the  controversy  as 
to  the  direct  formation  of  fat  from  protein  is  of  minor  im- 
portance, since  there  is  already  abundant  experimental  evi- 
dence of  the  production  of  carbohydrate  from  protein  and 
of  the  transformation  of  carbohydrate  into  fat,  so  that  it  is 
evident  that  protein  food  can  indirectly,  if  not  directly,  con- 
tribute to  the  formation  of  fat  in  the  body. 


no  CHEMISTRY    OF    FOOD    AND    NUTRITION 

The  Fate  of  the  Nitrogen  in  Protein  Metabolism.  —  The  fate 
of  the  nitrogen  of  the  protein  molecule  from  the  time  of  its 
absorption  until  it  reaches  the  forms  in  which  it  is  eliminated 
from  the  body  —  or,  as  it  is  now  commonly  called,  the  inter- 
mediary metaboHsm  of  protein  —  has  received  much  atten- 
tion during  the  past  few  years.  As  the  subject  is  still  under 
very  active  investigation,  it  seems  inadvisable  at  this  time  to 
attempt  to  summarize  the  results  as  a  whole,  and  for  the  pur- 
poses of  the  present  discussion  it  will  sufl5ce  to  consider  only 
so  much  of  the  fate  of  the  protein  nitrogen  as  is  shown  by 
the  more  important  end  products  eliminated  through  the 
kidneys. 

In  man  the  principal  end  product  is  urea,  but  together 
with  this  there  always  occurs  an  elimination  of  other  nitroge- 
nous compounds,  most  of  which  are  less  highly  oxidized  than 
urea.  These  less  highly  oxidized  end  products  are  of  interest 
from  different  points  of  view :  they  represent  a  loss  of  poten- 
tial energy  greater  than  that  which  would  occur  if  the  nitrogen 
were  eliminated  entirely  as  urea,  and  so  affect  the  estimation 
of  the  fuel  value  of  the  protein ;  they  may  to  some  extent  be 
regarded  as  intermediate  products  of  metabolism  of  protein, 
and  may  thus  throw  light  upon  the  changes  through  which  the 
nitrogen  of  protein  passed  before  reaching  the  urea  stage; 
considered  as  products  of  incomplete  metaboHsm,  they  may 
ser^^e  to  indicate  a  condition  of  diminished  power  of  oxidation, 
or  perhaps  more  frequently  a  condition  in  which  the  normal 
oxidizable   cleavage    products    are   not    formed    (probably 


THE    FATE    OF    THE    FOODSTUFFS    IN   METABOLISM       III 

through  failure  of  certain  hydrolytic  enzymes) ;  and  they 
may  be  regarded  as  imposing  an  additional  burden  upon  the 
organs  of  elimination.  The  protein  metabolism  has  generally 
been  considered  to  be  qualitatively  better  in  proportion  as  a 
larger  percentage  of  the  total  nitrogen  is  eliminated  as  urea 
and  a  smaller  percentage  in  other  forms.  This,  however, 
as  will  be  shown  below,  is  largely  a  matter  of  the  amount 
of  protein  consumed.  The  most  important  nitrogenous  end 
products  other  than  urea  are  ammonium  salts,  purin  bodies, 
and  creatinin.  Hippuric  acid  and  other  nitrogen  compounds 
are  normally  also  present  in  small  amounts. 

Urea.  —  The  proteins,  on  being  metabolized  in  the  body, 
yield  varying  amounts  of  arginin  which  may  undergo  hydroly- 
sis into  ornithin  and  urea.  In  this  way  an  appreciable  part 
of  the  nitrogen  of  protein  may  reach  the  urea  stage  through  a 
series  of  direct  cleavages.  It  is  altogether  probable,  however, 
that  the  greater  part  of  the  urea  eHminated  arises  as  follows : 
The  protein  in  katabolism  is  split  to  amino  acids,  which  are 
*'deaminized"  by  hydrolysis  as  in  the  conversion  of  alanin 
to  lactic  acid  above  mentioned,  the  nitrogen  of  the  amino 
group  being  split  out  as  ammonia,  which  with  the  carbonic 
acid  constantly  being  produced  in  metabolism  forms  ammo- 
nium carbonate.  Loss  of  one  molecule  of  water  yields  am- 
monium carbamate,  which  in  turn  on  loss  of  one  molecule  of 
water  yields  urea,  and  it  is  probable  that  the  greater  part  of 
the  urea  eliminated  is  formed  from  ammonium  carbonate  or 
carbamate  in  the  liver. 


112  CHEMISTRY    OF    FOOD    AND    NUTRITION 

(NH4)2C03  =  NH4CO2NH2  +  H2O. 

NH4CO2NH2  =  CO(NH2)2  +  H2O. 

Chloride  or  sulphate  of  ammonia  evidently  cannot  be 
changed  to  urea  in  this  way;  and  experiments  show  that  if 
hydrochloric  or  sulphuric  acid  is  introduced  into  the  blood,  it 
is  eUminated  by  the  kidneys  largely  as  ammonium  salt,  and 
the  quantity  of  urea  is  correspondingly  decreased.  In  dis- 
eased conditions  of  the  liver  the  organic  salts  of  ammonia 
(which  normally  should  be  burned  to  carbonate  and  then 
converted  as  above)  may  also  pass  through  and  be  eUminated 
without  being  changed  to  urea.  In  health  and  on  a  full  pro- 
tein diet  about  82  to  88  per  cent  of  the  total  nitrogen  excreted 
by  the  kidneys  is  usually  in  the  form  of  urea.  On  a  low 
protein  diet  the  percentage  is  lower. 

Ammonia.  —  As  already  noted,  ammonia  is  evidently  a 
normal  precxirsor  of  urea,  being  changed  to  the  latter  in  its 
passage  through  the  Hver.  In  accordance  with  this  view  we 
find  that  the  elimination  of  nitrogen  as  ammonia  may  be 
notably  increased  at  the  expense  of  urea:  (i)  in  structural 
diseases  of  the  Hver ;  (2)  after  injecting  mineral  acids  which 
combine  with  ammonia  in  the  body,  forming  stable  ammonium 
salts;  (3)  in  cases  of  a  pathological  excess  of  acids  in  me- 
tabolism, such  as  often  occurs  in  diabetes  and  in  fevers.  All 
of  these  are,  of  course,  abnormal  conditions.  Normally, 
about  2  to  6  per  cent  of  the  total  nitrogen  eliminated  is  in  the 
form  of  ammonium  salts,  the  amount  depending  largely  upon 
the  relation  between  the  amoimts  of  acid-forming  and  of 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   II3 

base-forming  elements  in  the  food,  which  will  be  discussed  in 
connection  with  the  study  of  the  ash  constituents  of  food  and 
of  mineral  metabolism. 

Uric  Acid  and  the  Purin  Bases.  —  The  formation  of  purin 
bases  in  the  cleavage  of  nucleo-protein  has  already  been  men- 
tioned. The  chemical  relations  of  these  bodies  to  each  other, 
to  uric  acid,  and  to  the  nucleus  purin  from  which  the  group 
takes  its  name  are  indicated  by  their  formulae :  — 

Purin,  C5H4N4. 

Adenin,  C5H3N4NH2        =  amino-purin. 
Guanin,  C5H3N4ONH2    =  amino-oxy-purin. 
Hypoxanthin,  C5H4N4O  =  oxy-purin. 
Xanthin,  C5H4N4O2         =  dioxy-purin. 
Uric  acid,  C5H4N4O3        =  trioxy-purin. 

Uric  acid  is  the  most  highly  oxidized  of  these  purins  and  is 
the  one  chiefly  found  in  the  urine.  In  man  and  other  mam- 
mals the  uric  acid  eliminated  comes  from  purin  bodies  which 
have  either  been  taken  as  such  in  the  food,  or  formed  in  the 
body  mainly  by  breaking  down  of  nucleo-protein,^  and  the 
proportion  of  nitrogen  given  off  in  this  form  may  be  varied 
enormously  by  changes  in  the  diet,  and  especially  in  the 
amounts  of  flesh  foods  eaten.  Usually  i  to  3  per  cent  of  the 
eHminated  nitrogen  will  be  found  in  the  form  of  uric  acid, 

1  It  is  possible  that  under  certain  (abnormal)  conditions  uric  acid  may 
also  be  formed  synthetically. 
I 


114  CHEMISTRY    OF   FOOD   AND   NUTRITION 

together  with  a  very  much  smaller  amount  in  the  form  of 
purin  bases.  So  much  of  the  uric  acid  as  arises  from  the 
metaboUsm  of  body  tissue  and  would  be  excreted  even  on  a 
purin-free  diet  (usually  about  0.3  to  0.4  gram  per  day)  is 
spoken  of  as  "endogenous,"  while  that  arising  from  the 
purins  of  the  food  is  called  "exogenous  "  uric  acid.  In  neither 
case,  however,  does  the  amount  excreted  represent  the  entire 
extent  of  the  purin  metaboUsm,  since  the  purin  bodies  formed 
in,  or  introduced  into,  the  body  are  oxidized  to  a  considerable 
extent.  The  extent  to  which  uric  acid  and  other  purins  are 
destroyed  in  the  body  varies  with  different  species  of  animals. 
The  human  body  in  health  oxidizes  about  one  half  of  the 
purins  introduced  and  excretes  about  one  half,  mainly  in  the 
form  of  uric  acid.  Recent  work  has  developed  the  successive 
steps  in  the  purin  metabolism  in  much  greater  detail  and 
shown  them  to  be  referable  to  specific  enzymes,  the  functions 
of  which  Lusk  gives  as  follows :  "  Summarizing  these  results, 
it  may  be  said  that  nucleic  acid  may  be  broken  up  by  nuclease, 
a  ferment  found  in  all  tissue.  On  the  liberation  of  the  purin 
bases,  guanin  and  adenin  are  deaminized  by  guanase  and 
adenase  wherever  these  enzymes  are  found.  Oxidizing  en- 
zymes, the  xanthin  oxidases,  now  convert  hypoxanthin  and 
xanthin  into  uric  acid,  while  a  uricolytic  ferment  of  varying 
potency  in  different  tissues  and  in  different  animals  rg^ay 
break  up  and  destroy  the  uric  acid."  Mendel,  as  the  result 
of  extended  investigation,  holds  that  the  formation  of  uric 
acid  takes  place  throughout  the  body  and  that  its  partial 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   II5 

destruction  is  accomplished  by  the  muscles,  the  kidneys,  and 
especially  by  the  liver. 

Creatinin. —  The  normal  urine  usually  contains  about  1.5 
grams  creatinin  per  day.  The  quantity  is  fairly  constant  for 
the  individual,  averaging  about  0.02  gram  per  kilogram  of 
body  weight  per  day.  The  origin  and  significance  of  creatinin 
and  especially  its  physiological  relations  to  creatin  (of  which 
it  is  chemically  the  anhydride)  is  still  unsettled,  despite  much 
recent  research.^  Since  the  amount  of  creatinin  excreted 
is  not  governed  by  the  amount  of  protein  consumed,  the  per- 
centage of  urinary  nitrogen  appearing  in  this  form  will  evi- 
dently increase  as  the  total  nitrogen  diminishes,  and  vice  versa. 
On  ordinary  mixed  diet  the  creatinin  nitrogen  usually  con- 
stitutes 3  to  7  per  cent  of  the  total  nitrogen  of  the  urine. 

The  above  statements  regarding  the  distribution  of  the 
eliminated  nitrogen  among  the  different  end  products  refer 
to  results  obtained  upon  an  ordinary  mixed  diet  containing 
the  usual  amount  of  protein.  Folin  has  shown  by  a  careful 
and  extended  study  of  the  urines  of  healthy  men  Hving  first 
upon  high  and  then  upon  low  protein  diets,  that  the  distri- 
bution of  the  nitrogen  between  urea  and  the  other  nitrogenous 
end  products  depends  very  largely  upon  the  absolute  amount 
of  nitrogen  metabolized.  In  the  case  of  a  man  who  on  one 
day  consumed  high  protein  diet  free  from  meat,  and  a  week 
later  was  Hving  on  a  diet  of  starch  and  cream,  which  furnished 

1  See  Lusk,  Science  of  Nutrition  (2d  ed.),  pp.  138-140,  for  outline  of 
recent  results  and  references  to  original  publications. 


ii6 


CHEMISTRY    OF   FOOD    AND    NUTRITION 


in  all  about  6  grams  of  protein  per  day,  the  distribution  of 
end  products  was  changed  as  shown  in  the  following  table :  — 


On  High  Protein  Diet 

On  Low  Protein  Diet 

(Free  from  Meat) 

(Starch  and  Cream) 

Grams 

Per  cent 

Grams 

Per  cent 

Total  nitrogen  .     .     . 

16.8 

3-6 

Urea  nitrogen   .     .     . 

14.7 

87.5 

2.2 

61.7 

Ammonia  nitrogen     . 

0.49 

3-0 

0.42 

"3 

Uric  acid  nitrogen      . 

0.18 

I.I 

0.09 

2.5 

Creatinin  nitrogen 

0.58 

3-6 

0.60 

17.2 

Undetermined  nitrogen 

0.85 

4.9 

0.27 

7.3 

Thus,  on  passing  from  the  high  protein  to  the  low  protein 
diet  (both  being  free  from  meat  products)  there  was  a  marked 
decrease  in  both  the  absolute  and  the  relative  amounts  of 
urea,  and  a  decrease  in  the  absolute,  but  increase  in  the  rela- 
tive, amount  of  uric  acid,  while  the  absolute  amount  of  crea- 
tinin remained  unchanged,  so  that  its  relative  amount  was 
greatly  increased. 


REFERENCES 

Abderhalden.     Textbook  of  Physiological  Chemistry. 

Armsby.     Principles  of  Animal  Nutrition,  Chapter  2, 

Chittenden.    The  Nutrition  of  Man,  Chapters  i  and  2. 

CoNNSTEiN.  Ueber  fermentative  Fettspaltung.  Ergehnisse  der  Physio- 
logic, 3,  I,  194-232  (1904). 

FoLiN.  A  Theory  of  Protein  Metabolism.  American  J ournal  of  Physi- 
ology, 13,  1 1 7-138. 

Hammarsten.    Textbook  of  Physiological  Chemistry. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM   II7 

Hill.     Recent  Advances  in  Physiology  and  Biochemistry,  Chapters  11 

and  12. 
Howell.     Textbook  of  Physiology,  Chapters  47  and  48. 
LusK.     The  Fate  of  the  Amino  Acids  in  the  Organism.    Journal  of  the 

American  Chemical  Society,  32,  671-680  (1910). 
Oppenheimer.     Handbuch  der  Biochemie,  4,  I. 
Von  Noorden.     Metabolism  and  Practical  Medicine,  Vol.  I,  pp.  64- 

127,153-168. 
Wells.     Chemical  Pathology,  Chapter  21  —  Uric  Acid  Metabolism. 


CHAPTER  V 

THE  FUEL  VALUE  OF  FOOD  AND  THE  ENERGY 
REQUIREMENT  OF  THE  BODY 

We  have  seen  that  carbohydrate  after  its  absorption  into 
the  body  may  be  burned  as  such,  or  stored  as  glycogen,  or 
transformed  into  fat;  that  fat  may  be  burned  or  stored  as 
such  and  probably  may  be  converted  into  carbohydrate; 
and  that  protein  may  either  be  used  as  such,  or  may  yield 
carbohydrate,  or  may  (either  directly  or  indirectly)  contribute 
to  the  production  of  fat.  It  has  also  been  shown  that  any  or 
all  of  these  foodstuffs  may  be  utilized  as  fuel  for  muscular 
work. 

These  facts  (as  well  as  others  which  will  appear  in  the 
chapters  which  follow)  make  it  plain  that  the  body  is  not 
restricted  to  the  use  of  any  one  foodstuff  for  the  support  of 
any  one  kind  of  work,  but  on  the  contrary  has  very  great 
power  to  convert  one  nutrient  into,  or  use  it  in  place  of,  an- 
other, and  so  to  utilize  its  resources  that  the  total  potential 
energy  of  all  of  these  nutrients  is  economically  employed  to 
support  the  work  of  all  parts  of  the  organism.  Thus  the 
carbohydrates,  fats,  and  proteins  stand  in  such  close  mutual 
relations  in  their  service  to  the  body  that  for  many  purposes 
we  may  properly  consider  the  food  as  a  whole  with  reference 

ii8 


THE   FUEL   VALUE    OF   FOOD  II9 

to  the  total  nutritive  requirements,  provided  a  common 
measure  of  values  and  requirements  can  be  found.  Since 
the  most  conspicuous  nutritive  requirement  is  that  of  energy 
for  the  work  of  the  body,  and  since  these  organic  nutrients  all 
serve  as  fuel  to  yield  this  energy,  the  best  basis  of  comparison 
is  that  of  fuel  value,  expressed  most  conveniently  in  terms  of 
calories. 

The  calorific  value  or  heat  of  combustion  of  any  substance, 
i.e.  the  amount  of  energy  liberated  by  the  burning  of  a  given 
quantity  of  the  combustible  material,  is  best  determined  by 
means  of  the  bomb  calorimeter  devised  by  Berthelot.  The 
particular  form  of  Berthelot  bomb  which  has  been  most  used 
in  the  examination  of  food  materials  and  physiological  prod- 
ucts is  that  of  Atwater  and  Blakeslee. 

This  instrument  and  the  method  of  its  use  have  been  fully 
described  by  Atwater  and  Snell  in  the  Journal  of  the  American 
Chemical  Society  for  July,  1903.  In  outline  it  consists  of  a 
heavy  steel  bomb  with  a  platinum  or  gold-plated  copper 
lining  and  a  cover  held  tightly  in  place  by  means  of  a  strong 
screw  collar.  A  weighed  amount  of  sample  is  placed  in  a 
capsule  within  the  bomb,  which  is  then  charged  with  oxygen 
to  a  pressure  of  at  least  20  atmospheres  (300  pounds  or  more 
to  the  square  inch),  closed,  and  immersed  in  a  weighed  amount 
of  water.  The  water  is  constantly  stirred  and  its  tempera- 
ture taken  at  intervals  of  one  minute  by  means  of  a  differ- 
ential thermometer  capable  of  being  read  to  one  thousandth 
of  a  degree.     After  the  rate  at  which  the  temperature  of  the 


I20  CHEMISTRY    OF   FOOD    AND   NUTRITION 


Fig.  3.  —  Bomb  calorimeter;    appar..    .-  ...    .  .  .  .   r    . .  . ; nnnations  of  heats  of 

combustion.     (Atwater  and  Blakeslee.) 


THE  FUEL  VALUE  OF  FOOD  121 

water  rises  or  falls  has  been  determined,  the  sample  is  ignited 
by  means  of  an  electric  fuse,  and,  on  account  of  the  large 
amount  of  oxygen  present,  undergoes  rapid  and  complete 
combustion.  The  heat  liberated  is  communicated  to  the 
water  in  which  the  bomb  is  immersed  and  the  resulting  rise  in 
temperature  is  accurately  determined.  The  thermometer 
readings  are  also  continued  through  an  "after  period,"  in 
order  that  the  "radiation  correction"  may  be  calculated  and 
the  observed  rise  of  temperature  corrected  accordingly. 
This  corrected  rise,  multiplied  by  the  total  heat  capacity  of 
the  apparatus,  and  the  water  in  which  it  is  immersed,  shows 
the  total  heat  hberated  in  the  bomb.  From  this  must  be 
deducted  the  heat  arising  from  accessory  combustions  (the 
oxidation  of  the  iron  wire  used  as  a  fuse,  etc.)  to  obtain  the 
number  of  calories^  arising  from  the  combustion  of  the  sample. 

The  heat  of  combustion  of  organic  substances  is  closely 
connected  with  their  elementary  composition.  One  gram 
of  carbon  burned  to  carbon  dioxide  yields  8.08  calories  and 
I  gram  of  hydrogen  burned  to  water  yields  34. 5  calories.  If 
a  compound  consisting  of  carbon  and  hydrogen  only  be  burned, 
it  gives  nearly  the  amount  of  heat  which  these  would  give  if 
burned  separately. 

On  the  other  hand,  carbohydrates  and  fats,  being  com- 

^  When  the  term  "calorie"  is  used  in  this  work  it  will  be  understood 
to  mean  the  greater  calorie,  i.e.  the  amount  of  heat  required  to  raise  the 
temperature  of  one  kilogram  of  water  one  degree  centigrade.  This  is  very 
nearly  the  same  as  the  heat  required  to  raise  four  pounds  of  water  one 
degree  Fahrenheit. 


122  CHEMISTRY    OF    FOOD    AND    NUTRITION 

posed  of  carbon,  hydrogen,  and  oxygen,  the  carbon  and  hydro- 
gen are  already  partly  oxidized  by  the  oxygen  present  in  the 
molecule ;  so  that  loo  grams  of  glucose,  for  example,  contain- 
ing 40  grams  carbon,  6.7  grams  hydrogen,  and  53.3  grams 
oxygen,  would  yield  considerably  less  heat  than  would  be 
obtained  by  burning  40  grams  of  pure  carbon  and  6.7  grams 
of  pure  hydrogen  to  carbon  dioxide  and  water  respectively. 

Proteins  when  burned  in  the  calorimeter  give  off  their 
carbon  as  carbon  dioxide,  their  hydrogen  as  water,  and  their 
nitrogen  as  nitrogen  gas.  Thus  the  nitrogen  contributes 
nothing  to  and  takes  nothing  from  the  heat  of  combustion;  and 
the  latter  is  dependent  here,  as  in  the  case  of  carbohydrates 
and  fats,  upon  the  amount  of  carbon  and  hydrogen  present 
and  the  extent  to  which  they  are  already  combined  with  oxy- 
gen. A  little  additional  heat  is  obtained  by  the  burning  of 
the  small  amount  of  sulphur  present  in  the  protein. 

The  relation  between  the  elementary  composition  and  heat 
of  combustion  will  be  made  clearer  by  the  following  table, 
which  includes  a  number  of  typical  compounds  found  in  the 
food  or  formed  in  the  body. 


THE    FUEL   VALUE    OF    FOOD 


123 


Heats  of  Combustion  and  Approximate  Elementary  Composition 
OF  Typical  Compounds 


Heat  of 
Combus- 
tion 
Calories 
PER  Gram 

Carbon 

PER 

Cent 

Hydro- 
gen 

PER 

Cent 

Oxygen 

PER 

Cent 

Nitro- 
gen 

PER 

Cent 

Sul- 
phur 

PER 

Cent 

Phos- 
phorus 

PER 

Cent 

Glucose  .     .     . 

3-75 

40.0 

6.7 

53-3 

Sucrose  . 

3-96 

42.1 

6.4 

51-5 

Starch       1 
Glycogen  j 

4.22 

44.4 

6.2 

49.4 

Body  fat 

9.60 

76.S 

12.0 

ii.S 

Butter  fat 

9-30 

75-0 

II. 7 

13-3 

Edestin  . 

5-64 

51-4 

7.0 

22.1 

18.6 

0.9 

Legumin 

5-62 

51-7 

7.0 

22.9 

18.0 

0.4 

Gliadin  . 

5-74 

52.7 

6.9 

21.7 

17.7 

I.O 

Casein    . 

5.85 

53-1 

7.0 

22.5 

15-8 

0.8 

0.8 

Albumin 

5.80 

52.S 

7.0 

23.0 

16.0 

1-5 

Gelatin  . 

5-30 

50.0 

6.6 

24.8 

18.0 

0.6 

Creatinin 

4.58 

42.5 

6.2 

14.1 

37-2 

Urea  .     . 

2.53 

20.0 

6.7 

26.7 

46.6 

Since  the  body  gets  its  energy  from  the  oxidation  of  the 
same  kinds  of  compounds  which  exist  in  foods,  that  is,  es- 
sentially from  carbohydrates,  fats,  proteins,  and  their  cleav- 
age products,  if  we  know  the  kinds  and  amounts  of  foodstuffs 
eaten  and  the  extent  to  which  they  are  oxidized  in  the  body, 
we  can  estimate  in  terms  of  calories  the  amount  of  energy 
hberated. 

The  average  heats  of  combustion  are :  — 

Carbohydrates  4.1    cal.  per  gram. 

Fats  9.45  cal.  per  gram. 

Protein  (nitrogen  X  6.25)      5.65  cal.  per  gram. 


124  CHEMISTRY    OF   FOOD   AND    NUTRITION 

In  the  body  carbohydrates  and  fats  burn  to  the  same  products 
as  in  the  calorimeter  and  so  yield  the  same  amounts  of  heat. 
Protein,  however,  which  burns  in  the  bomb  to  carbon  dioxide, 
water,  and  nitrogen,  yields  in  the  body  no  free  nitrogen  but 
urea  and  other  organic  nitrogen  compounds  which  are  elimi- 
nated as  end  products  (see  the  preceding  chapter).  These 
organic  nitrogenous  end  products  are  combustible ;  they  rep- 
resent a  less  complete  oxidation  of  protein  in  the  body  than 
takes  place  in  the  bomb.  The  loss  of  potential  energy  calcu- 
lated on  the  assumption  that  all  nitrogen  left  the  body  as  urea 
would  be  about  0.9  calories  per  gram  of  protein;  but  on  ac- 
count of  the  elimination  of  other  substances  of  higher  heat  of 
combustion  (creatinin,  uric  acid,  etc.),  the  actual  loss  in  the 
form  of  combustible  end  products  is  considerably  greater  and 
averages  about  1.3  calories  for  each  gram  of  protein  broken 
down  in  the  body  (equivalent  to  about  1.2  calories  for  each 
gram  of  protein  in  the  food). 

Hence,  when  the  body  burns  material  which  it  has  pre- 
viously absorbed,  it  obtains :  — 

From  carbohydrates  4.1    cal.  per  gram. 

From  fats  9.45  cal.  per  gram. 

From  protein  (5.65  —  1.30  =  )  4.35  cal.  per  gram. 

In  calculating  the  fuel  value  of  the  food,  however,  allow- 
ance must  be  made  for  the  fact  that  a  part  of  each  of  the  ma- 
terials is  lost  in  digestion.^ 

^  The  expression  " lost  in  digestion"  is  here  used  in  the  sense  explained 
in  Chapter  III. 


THE  FUEL  VALUE  OF  FOOD  1 25 

The  approximate  averages  on  mixed  diet  are :  — 

Carbohydrates  2  %  lost,  98  %  absorbed. 
Fats  5  %  lost,  95  %  absorbed. 

Protein  8  %  lost,  92  %  absorbed. 

The  ap|proximate  physiological  fuel  values  of  the  food  con- 
stituents are  then :  — 

Carbohydrates  4.1    X  98  %  =  4.  calories  per  gram. 
Fats  9.45  X  95  %  =  9.  calories  per  gram. 

Protein  4.35  X  92  %  =  4.  calories  per  gram. 

The  figures  given  by  Rubner  as  representing  the  fuel  values 
of  food  constituents  are  as  follows :  — 

Carbohydrates  4.1 
Fats  9.3 

Protein  4.1 

These  were  derived  from  experiments  with  dogs  fed  on 
meat,  starch,  sugar,  etc.,  and  therefore  do  not  allow  for  so 
much  loss  in  digestion  as  has  been  found  to  occur  with  men 
living  on  ordinary  mixed  diet. 

FUEL  VALUE   OF   FOOD 

If  the  composition  of  a  food  is  known,  its  approximate  fuel 
value  is  easily  computed  by  means  of  the  above  factors.  Thus 
milk  of  about  average  grade  contains :  — 

Protein,  7,.^  per  cent;  fat,  4.0  per  cent;  carbohydrate,  5.0 
per  cent. 


126  CHEMISTRY    OF    FOOD    AND    NUTRITION 

One  hundred  grams  of  such  milk  will  furnish  in  the  form  of 
protein  (3.3  X  4.  =)  13.2  calories,  of  fat  (4.0  X  9.  =)  36.0 
calories,  of  carbohydrate  (5.0  X  4.  =)  20.0  calories;  total 
for  100  grams  of  milk,  69.2  calories. 

Eggs  contain  ^  on  the  average,  in  the  edible  portion,  13.4 
per  cent  protein,  10.5  per  cent  fat,  and  no  appreciable 
amount  of  carbohydrate.  They  would  then  furnish  per  100 
grams  (13.4  X  4)  +  (10.5  X  9)  =  148. i  calories. 

Milk  and  eggs  are  suflficiently  similar  to  be  used  interchange- 
ably in  the  adult  dietary  mthin  reasonable  limits,  but  evi- 
dently they  furnish,  weight  for  weight,  very  different  amounts 
of  nutrients  and  energy.  A  unit  weight  of  material  is  there- 
fore not  a  satisfactory  basis  of  comparison  in  foods.  Neither 
would  equal  weights  of  dry  matter  be  equivalent,  for  a  gram 
of  egg  solids  would  have  somewhat  more  food  value  than  a 
gram  of  milk  solids.  Ordinarily  the  quantities  to  be  taken  as 
equivalent  or  mutually  replaceable  are  those  which  furnish 
equal  fuel  value,  e.g.  loo-calorie  portions,  the  weights  of 
which  may  be  calculated  directly  from  the  fuel  values  of  100 
grams. 

Thus,  for  milk  —  100  grams  furnish  69.2  calories ;  then,  if  x 
be  the  number  of  grams  which  furnish  100  calories:  — 

100 :  69.2  : :  a; :  100;      x  =  145.^ 

^  These  and  all  similar  statements  of  average  composition  are  based  on 
Bull.  28,  Office  of  Experiment  Stations,  U.  S.  Dept.  Agricultm-e. 

2  It  is  considered  sufficiently  accurate  to  state  these  quantities  to  the 
nearest  whole  number  of  grams. 


THE  FUEL  VALUE  OF  FOOD  1 27 

Similarly  for  eggs :  — 

100 :  148  '.:x:  100;     x  =  68. 

And  since  the  two  extremes  in  the  proportion  are  always  the 
same,  the  weight  in  grams  of  the  loo-calorie  portion  may 
always  be  found  by  dividing  10,000  (the  product  of  the 
extremes)  by  the  number  of  calories  per  100  grams. 

The  fuel  value  of  foods  is  often  stated  in  calories  per  pound. 
Thus  in  the  same  table  (Bull.  28)  from  which  the  above  figures 
for  composition  are  taken,  the  fuel  value  of  milk  is  given 
as  325  calories  per  pound.  Since  453.6  grams  furnish  325 
calories,  — 

453-6 :  325  :•  ^  •'  100;     ^  =  i39-6, 

the  number  of  grams  required  to  furnish  100  calories.  This 
figure  is  about  3  per  cent  less  than  the  one  found  above 
because  it  is  based  on  a  fuel  value  computed  by  Rubner's 
factors,  which  are  2.5  to  t^.t,  per  cent  higher  than  the  factors 
based  on  more  recent  work.      (See  above.) 

The  following  figures  for  a  few  common  food  materials 
are  based  upon  the  more  recent  factors,  and  show  the  weight 
of  the  loo-calorie  portion  in  grams  and  ounces,  and  the  dis- 
tribution of  the  calories  between  proteins,  fats,  and  carbo- 
hydrates :  — 


128 


CHEMISTRY    OF   FOOD   AND    NUTRITION 


Table  of  ioo-Calorie  Portions  of  Food  Material  based  on  the 
Factors  —  Protein,  4 ;  Fat,  9  ;  Carbohydrate,  4 


Food  Material  (Edible 
Portion) 


Weight  of  Portion 


Grams        Ounces 


Distribution  of  Calories 


In  protein 


In  fat 


Beef,  free  from  visible  fat 
Beef,  round  steak  .  .  . 
Beef,  corned      .... 

Ham,  lean 

Ham,  fat 

Bacon,  smoked  .... 

Codfish 

Salmon 

Eggs 

Milk 

Butter 

Com  meal 

Oatmeal 

Rice 

WTieat,  "entire"    .     .     . 

\\Tieat  flour 

Bread,  white      .     .     .     . 

Sugar  

Asparagus 

Beans,  dried  .  .  .  . 
Beans,  string      .     .     .     . 

Beets 

Cabbage   

Carrots 

Celery 

Com,  green  or  canned    . 

Lettuce 

Potatoes 

Spinach 


86 
64 
33 

37 

■  » 

16 
143 
49 
67 
145 
14 
27 

25 

28 

28 

28 

38 

25 

450 

29 

240 

216 

317 
220 
540 
99 
523 
120 
418 


3-0 
2-3 
1-3 
1.2 
0.7 
0.6 
5-0 
1-7 
2.3 
5-1 
o.S 
i.o 
0.9 
1.0 
1.0 
1.0 

1-3 
0.9 

16.0 
1.0 
8.4 
7.4 

II. I 

7-7 
19.1 

3-2 
18.4 

4.2 
14.7 


80.4 

54.5 
20.9 
29.7 
II. I 
6.7 
95-0 
43-3 
36.1 

19-e 

0.5 

9.0 

16.1 

9.1 

14.7 

11.8 

14.1 

32.4 
26.1 
22.2 
13.8 
20.3 
9-7 
23.8 
12.2 
25.2 
10.5 
351 


19.6 

45-5. 
79.1 

70.3 
88.9 

93-3 
50 
56.7 
639 
52.D 

99-5 

11.4 

16.2 

0.7 

3-5 
2.8 

4-5 

8.2 
4-7 
6.5 
2.0 
8.6 

7-9 
4.8 
9.8 

14.1 
1.2 

II-3 


THE    FUEL   VALUE    OF   FOOD 


129 


Food  Material  (Edible 
Portion) 


Weight  of  Portion 


Grams 


Ounces 


Distribution  of  Calories 


n  protein 


In  fat 


In  carbo- 
hydrates 


Tomatoes 

Turnips     .  . 

Apples       ,  . 

Bananas   .  . 
Currants,  dried 

Oranges    .  . 

Peaches     .  . 
Pineapple 

Plums       .  . 
Prunes,  dried 

Raisins      .  . 
Almonds 
Chestnuts 

Peanuts    .  . 

Olive  Oil  .  . 


438 
253 
159 

lOI 

31 
194 
242 
232 
118 

33 
29 

IS 
43 
18 
II 


iS-5 
8.9 
5-6 
3-5 
I.I 
6.8 

8.5 
8.2 
4.1 
1.2 
i.o 
0.5 
1-5 
0.6 
0.4 


iS-7 
13.2 

2-5 

5.2 
3-0 
6.2 
6.8 
3-7 
4-7 
2.8 

3-0 
13.0 
10.7 
18.8 


15-7 
4.6 

7.2 
5.4 
4-7 
3-5 
2.2 

6.3 


8.6 
76.4 
16.6 
63-4 

lOO.O 


68.6 
82.2 
90-3 
89.4 
92.3 
90-3 
91.0 
90.0 

95-3 
97.2 
88.4 
10.6 
72.7 
17.8 


Since  proteins  and  carbohydrates  have  the  same  average 
fuel  value  and  the  ash  of  food  usually  does  not  constitute  a 
large  percentage,  the  striking  differences  in  the  weights  of  the 
various  foods  required  to  furnish  100  calories  are  usually 
referable  to  differences  in  water  content  or  fat  content  or  both. 
That  beans  have  nearly  20  times  the  fuel  value  of  celery  is 
essentially  due  to  the  difference  in  moisture,  while  the  differ- 
ence in  fuel  value  between  lean  beef  and  bacon,  or  between 
codfish  and  salmon,  is  chiefly  a  matter  of  fat  content.  Meat 
free  from  fat  is  about  three-fourths  water  and  one-fourth  pro- 
tein and  so  has  a  fuel  value  of  about  one  calorie  per  gram,  while 
clear  fat  has  a  fuel  value  about  nine  times  as  great. 


130  CHEMISTRY    OF   FOOD    AND    NUTRITION 

Fuel  values  of  meats  as  given  in  the  standard  tables  are  apt 
to  be  somewhat  misleading,  inasmuch  as  they  allow  for  all  the 
fat  ordinarily  found  on  the  various  cuts  as  taken  from  the 
animal,  whereas  in  many  cases  a  considerable  part  of  this  fat 
is  trimmed  off  by  the  butcher  and  treated  as  a  by-product ; 
and  often  much  of  the  remaining  layers  of  fat  is  removed  either 
in  the  kitchen  or  at  the  table.  If  a  pound  of  steak  consists 
of  14  ounces  of  clear  lean,  and  2  ounces  of  clear  fat,  and  the  fat 
is  not  eaten,  at  least  half  of  the  total  fuel  value  of  the  pound 
of  steak  is  lost. 

Many  vegetables  are  more  watery  than  lean  meats  and  so 
contrast  even  more  strikingly  with  the  fats.  An  ounce  of  clear 
fat  pork  is  equal  in  fuel  value  to  about  two  pounds  of  cabbage ; 
an  ounce  of  olive  oil  to  over  three  pounds  of  lettuce. 

In  connection  with  such  comparisons  of  fuel  value,  how- 
ever, it  should  be  emphasized  that  the  fuel  value  of  a  food, 
while  of  primary  importance,  is  not  alone  a  complete  measure 
of  its  nutritive  value,  which  will  depend  in  part  also  upon  the 
amounts  and  forms  of  nitrogen,  phosphorus,  iron,  and  various 
other  essential  elements  furnished  by  the  food. 

In  order  to  indicate  relative  richness  in  nitrogenous  constit- 
uents (protein),  it  is  not  uncommon  to  state  the  "nutritive 
ratio"  along  with  the  fuel  value  of  a  food.  The  "  nutritive 
ratio"  or  "nutrient  ratio"  is  the  ratio  of  nitrogenous  to  non- 
nitrogenous  nutrients,  compared  on  the  basis  of  fuel  values. 
Since  the  fuel  values  of  carbohydrates  and  protein  are  taken  as 
equal  (4  calories  per  gram),  and  that  of  fats  as   2^  times 


THE   FUEL   VALUE    OF   FOOD  131 

as  great  (9  calories  per  gram),  the  nutritive  or  nutrient  ratio 
may  be  shown  as  follows  :  — 

Protein  :  Carbohydrate  +  2\  Fat : :  i:  x  ; 
or  the  ratio  may  be  expressed  in  the  form  of  a  fraction  :  — 

Carbohydrate  +  2I  Fat  * 
Protein 

These  expressions  can,  of  course,  be  applied  equally  well  to 
percentages  or  to  weights  of  nutrients. 

The  same  information  as  is  given  by  the  statement  of  fuel 
value  per  pound  and  nutritive  ratio  may  be  obtained  by  com- 
paring the  weight  of  loo-calorie  portions  and  the  percentages 
of  calories  supplied  by  protein  as  shown  in  the  above  table. 
The  statement  that  19  per  cent  of  the  calories  of  milk  are  fur- 
nished by  protein  is  equivalent  to  giving  the  nutritive  ratio  of 
milk  as  i :  4.3. 

So  far  as  concerns  merely  the  protein  and  energy  values  of  a 
dietary,  foods  which  show  similar  percentages  of  calories  from 
protein  are  interchangeable  in  the  quantitative  proportions 
indicated  by  the  weights  of  the  loo-calorie  portions.  It 
thus  becomes  easy  to  determine  which  is  really  the  more  eco- 
nomical of  any  two  foods  which  may  be  regarded  as  inter- 
changeable in  the  dietary.  If  the  foods  are  in  fact  interchange- 
able, then  that  one  will  be  more  economical  which  furnishes 
more  calories  for  a  given  expenditure. 


132  CHEMISTRY    OF    FOOD   AND    NUTRITION 

ENERGY  REQUIREMENT  IN  METABOLISM  —  METH- 
ODS OF  STUDY  AND  AMOUNTS  REQUIRED  FOR 
MAINTENANCE  AT  REST 

We  know  definitely  from  accurate  experiments  that  the 
"physiological  fuel  values"  which  have  been  deduced  repre- 
sent the  energy  which  is  actually  obtained  by  the  body  from 
the  food  and  which  appears  as  muscular  work  or  as  heat; 
and  we  have  every  reason  to  suppose  that  under  ordinary 
conditions  the  carbohydrates,  fats,  and  proteins  each  supply 
the  body  with  the  kinds  of  energy  needed  for  its  maintenance 
and  for  its  work,  approximately  in  proportion  to  their  fuel 
values  as  calculated  above.  We  do  not  now  believe  that  any 
one  nutrient  is  used  to  the  exclusion  of  others  as  a  source  of 
energy  for  any  particular  function,  nor  indeed  that  the  body 
makes  any  particular  distinction  between  the  foodstuffs  as 
sources  of  energy.  The  fuel  value  of  the  diet  as  a  whole 
is  utilized  to  meet  the  energy  requirements  of  the  whole 
body.  For  the  present,  therefore,  it  is  the  fuel  value  of 
the  day's  dietary  which  we  have  to  consider  rather  than 
the  distribution  of  this  as  regards  protein,  fats,  and  carbo- 
hydrates. 

The  total  food  (or  energy)  requirement  is  best  expressed  in 
calories  per  day,  either  for  the  whole  body  or  per  kilogram  of 
body  weight,  and  for  convenience  of  discussion  it  is  usually 
assumed  that  the  average  body  weight  (without  clothing  ^)  is 

*  The  average  weight  of  a  man's  clothing  is  usually  estimated  at 
about  10  poimds ;  of  a  woman's,  about  8  pounds. 


THE  FUEL  VALUE  OF  FOOD  1 33 

for  men  70  kilograms  (154  pounds)  and  for  women  eight  tenths 
as  much,  56  kilograms  (123  pounds). 

There  are  four  important  methods  of  studying  the  food 
requirements  of  man  :  ^  — 

1.  By  observing  the  amount  of  food  consumed   (dietary 

studies). 

2.  By  observing  the  amount  of  oxygen  consumed  —  pref- 

erably also  the  respiratory  quotient  (respiration  ex- 
periments). 

3.  By  determining  the  balance  of  intake  and  output  (car- 

bon and  nitrogen  metabolism  experiments). 

4.  By  direct  measurement  of  heat  given  off  by  the  body 

(calorimeter  experiments). 

Dietary  Studies.  —  Most  dietary  studies  give  little  more 
than  a  general  indication  of  the  food  habits  of  the  people 
studied;  but  in  cases  where  persons  have  maintained  for  a 
long  time  the  same  dietary  habits  and  other  conditions  of  life, 
and  the  body  weight  has  remained  practically  constant, 
it  may  be  fairly  safe  to  assume  that  the  food  has  furnished 
just  about  the  right  amount  of  energy  for  the  maintenance  of 
the  body  under  the  observed  conditions. 

Great  care  must  be  taken  in  drawing  inferences  from  the 
body  weight  because  of  the  readiness  with  which  the  body 
gains  or  loses  moisture.     Athletes  often  lose  2  or  3  pounds  in 

*  For  an  account  of  the  historical  development  of  the  principles  which 
underlie  the  measurement  of  metabolism,  see  the  introductory  chapter 
of  Lusk's  Elements  of  the  Science  of  Nutrition, 


134  CHEMISTRY   OF   FOOD   AND   NUTRITION 

an  hour  of  vigorous  exercise  and  regain  it  in  less  than  a  day. 
Gain  or  loss  of  body  weight  during  short  periods,  therefore, 
does  not  by  any  means  necessarily  imply  a  corresponding 
gain  or  loss  of  fat.  The  body  may  lose  fat  and  at  the  same 
time  maintain  its  weight  through  gaining  water,  or  vice  versa. 
When,  however,  the  weight  remains  nearly  the  same  for 
months  at  a  time,  it  may  usually  be  assumed  that  there  is  no 
important  gain  or  loss  of  tissue  and  that  the  body  is  receiv- 
ing just  about  the  proper  amount  of  total  food  for  its 
needs.  Under  these  conditions  an  accurate  observation  of 
the  food  consumed  may  give  valuable  indications  as  to  the 
actual  food  requirement.  Of  such  dietary  studies  perhaps 
the  most  useful  individual  example  is  that  of  Neumann,  who 
reduced  his  diet  to  what  appeared  to  be  just  about  sufficient 
for  his  needs  and  then  recorded  all  food  and  drink  taken  dur- 
ing a  period  of  lo  months  in  which  the  body  weight  was  nearly 
constant  but  showed  a  slight  gain.  The  average  daily  food 
furnished :  ^  — 


Nutrients  Factors  Calories 


Total  Calories 
PER  Day 


Protein 66.1  grams   X  4.    =    264.4 

Fat 83.5  grams   X  9.    =    751.5     [      2242 

Carbohydrate  2     .     .     .  306.5  grams   X  4.    =1226.0     ] 

The  2242  calories  per  day  were  e\adently  fully  sufficient 
to  meet  the  energy  requirements  of  this  man,  whose  weight 

1  The  data  are  taken  from  Chittenden's  Nutrition  of  Man,  p.  286. 

'  Including  some  alcohol  (taken  in  the  form  of  beer),  which  is  esti- 
mated as  equivalent  in  fuel  value  to  1.75  times  its  weight  of  carbohy- 
drates. 


THE  FUEL  VALUE  OF  FOOD  135 

was  66.5  to  67  kilograms  (about  147  pounds)  and  who  was  en- 
gaged at  his  usual  (mainly  sedentary)  professional  work  in 
the  Hygienic  Institute  at  Kiel. 

Later,  when  his  weight  had  increased  to  71.5  kilograms 
(157  pounds)  as  the  result  of  following  for  a  time  a  more  lib- 
eral diet  (furnishing  about  2600  calories  per  day),  he  again 
observed  his  dietary  while  taking  what  was  supposed  to  be  an 
amount  of  food  sufficient  for  the  maintenance  of  the  body 
and  no  more.  This  second  dietary  study  was  continued  for 
8  months,  during  which  the  average  daily  food  consumption 
was  found  to  be :  — 

Nutrients  Factors  Calories  '^°'"^^^'f  ^^ 

Protein 76.2  grams  X  4.  =  304.8  1 

Fat 109.0  grams  X  9.  =  981.0   \       2000 

Carbohydrates  1  ....  178.6  grams  X  4.  =  714-4  J 

These  results  indicate  that  this  subject,  a  man  of  average 
size,  living  a  normal  professional  life  involving  no  manual 
labor  in  the  ordinary  sense,  but  not  excluding  such  muscular 
movements  as  are  naturally  incidental  to  a  sedentary  occupa- 
tion, found  his  energy  requirements  satisfied  with  food  furnish- . 
ing  2000  to  2250  calories  per  day. 

Respiration  Experiments.  —  Since  the  foodstuffs  yield  their 
energy  through  being  burned  in  the  body,  i.e.  by  uniting  with 
oxygen,  it  is  evident  that  a  measure  of  the  energy  metabolism 
can  be  obtained  by  finding  either  the  amount  of  foodstuffs 

^  Including  some  alcohol  (taken  in  the  form  of  beer),  which  is  estimated 
as  equivalent  in  fuel  value  to  1.75  times  its  weight  of  carbohydrates. 


136  CHEMISTRY    OF    FOOD    AND    NUTRITION 

or  the  amount  of  oxygen  which  is  consumed  in  the  process. 
The  apparatus  devised  and  used  by  Zuntz  ^  for  this  purpose 
provides  a  mask  fitting  air-tight  over  the  mouth  and  nose  and 
connected  by  means  of  valved  pipes  with  apparatus  for  meas- 
uring and  analyzing  the  inspired  and  expired  air.  In  this 
way  one  can  determine  the  volume  of  oxygen  entering,  and 
the  volimie  leaving,  the  lungs.  The  difference  is  the  volume 
consimied  in  the  body. 

A  given  volume  of  oxygen  used  in  the  body  may  liberate 
somewhat  different  amounts  of  heat,  according  as  it  oxidizes 
fat,  carbohydrate,  or  protein. 

1000  CO.  oxygen  bum  ap- 
proximately   .     .     .     .0.5    gram  fat,  jdelding  4.7  calories. 

1000  cc.  oxygen  bum  ap- 
proximately   ....  i.34gramsglucose,  yielding  5.0  calories. 

1000  cc.  oxygen  burn  ap- 
proximately   ....  1.05  grams  protein,  yielding  4.6  calories. 

For  accurate  estimations  of  the  energy  liberated  it  is  there- 
fore necessary  to  know  the  kind  of  material  oxidized,  as  well 
as  the  amount  of  oxygen  consumed.  This  is  accomplished  by 
measuring  the  volume  of  carbon  dioxide  evolved  as  well  as  of 
oxygen  consumed,  and  calculating  the  respiratory  quotient. 

Since  the  amount  of  protein  broken  dowTi  in  the  body  can 
be  found  by  other  methods  as  described  below,  the  determina- 

1  For  description  of  a  new  form  of  apparatus  for  studying  the  respira- 
tory exchange  see  Benedict,  American  Journal  of  Physiology,  24,  545 
(1909). 


THE  FUEL  VALUE  OF  FOOD  137 

tion  of  the  respiratory  quotient  along  with  the  oxygen  con- 
sumption shows  the  extent  of  the  combustion  in  the  body  and 
the  proportions  of  fat  and  carbohydrate  burned.  From  these 
data  the  energy  hberated  can  be  calculated. 

This  method  of  studying  the  total  metabolism  permits  of 
experiments  being  carried  out  very  quickly,  and  is  therefore 
especially  useful  for  the  direct  investigation  of  conditions 
w^hich  affect  metabolism  at  once,  e.g.  muscular  work,  work  of 
digestion,  etc.  Moreover,  the  apparatus  can  be  made  port- 
able and  thus  be  carried  by  the  subject  like  a  knapsack  in 
experiments  on  marching,  mountain  climbing,  or  bicycling. 
The  observations  cannot  be  made  continuous,  but  the  prob- 
able results  for  the  24  hours'  metabolism  can  be  estimated  by 
the  data  obtained  during  frequent  short  periods  at  different 
times  of  the  day  and  night.  For  a  critical  comparison  of  this 
method  with  the  Pettenkofer  and  Voit  method  of  studying 
metabolism  by  the  determination  of  the  carbon  balance,  the 
reader  is  referred  to  the  discussion  by  Magnus-Levy  in  Von 
Noorden's  Metabolism  and  Practical  Medicine,  Vol.  I,  pp. 
186-198. 

From  the  results  of  many  observations  by  this  method,. 
Magnus-Levy  estimates  the  minimum  metabolism  of  a  man 
of  average  size  kept  absolutely  motionless  and  fasting  at 
1625  calories  per  day.  Food  barely  sufficient  for  maintenance 
would  increase  this  by  175,  and  such  incidental  muscular 
movements  as  would  ordinarily  be  made  by  a  man  at  rest  in 
bed  would  involve  another  200,  making  a  total  of  2000  calo- 


138  CHEMISTRY    OF    FOOD    AND    NUTRITION 

lies  as  the  estimated  food  requirement  of  a  man  at  rest  with 
a  maintenance  diet.  Magnus-Levy  further  estimates  that 
the  man,  if  doing  no  work  (in  the  ordinary  sense),  but  allowed 
to  move  about  the  room  instead  of  remaining  in  bed,  would 
require  2230  calories  per  day. 

Metabolism  or  Balance  Experiments.  —  By  determining 
the  constituents  of  the  food  consumed  and  of  the  substances 
eUminated  from  the  body,  the  material  actually  oxidized  and 
the  energy  Uberated  in  the  oxidation  can  be  found  by  a  com- 
parison of  the  intake  and  output. 

The  "intake"  is  found  by  weighing  and  analyzing  all  food 
eaten;  the  "output"  by  collecting  and  determining  the  end 
products  eliminated  through  the  lungs,  the  kidneys,  the  in- 
testines, and  sometimes  (in  very  exact  experiments)  the  skin. 
The  time  unit  in  experiments  upon  the  intake  and  output  is 
almost  always  24  hours,  the  experimental  day  beginning 
preferably  just  before  breakfast.  The  intestinal  residues 
belonging  to  the  experimental  days  are  marked  and  separated 
usually  by  gi\ing  a  small  amount  of  lampblack  with  the  food 
as  in  ordinary  digestion  experiments,  while  the  end  products 
given  off  by  the  lungs  and  kidneys  during  an  experimental 
day  are  taken  as  measuring  the  material  broken  down  in  the 
body  during  the  same  period.  In  the  case  of  the  carbon  diox- 
ide given  off  by  the  lungs,  there  can  be  very  Httle  error  in  this 
assumption,  for  carbon  dioxide  is  eHminated  almost  as  rapidly 
as  it  is  formed,  and  if,  on  account  of  exercise  or  for  any  other 
reason,  the  formation  should  exceed  the  eUmination  during 


THE  FUEL  VALUE  OF  FOOD 


139 


the  active  part  of  the  day,  any  excess  of  carbon  dioxide 
left  in  the  body  would  almost  certainly  be  given  off  during 
the  night. 

More  time  is  of  course  required  for  the  elimination  of  the 
nitrogenous  end  products  through  the  kidneys.  This  un- 
avoidable "lag"  in  the  ehmination  of  nitrogen  may  intro- 
duce an  error  in  determining  the  nitrogen  balance  unless  the 
subject  has  been  kept  for  a  few  days  in  advance  upon  the 
same  diet  which  is  to  be  used  in  the  experiment. 

Assuming  that  the  total  nitrogen  and  carbon  of  the  ab- 
sorbed food  existed  in  the  form  of  protein,  fat,  and  carbo- 
hydrate, and  that  the  amount  of  carbohydrates  in  the  body  is 
constant  from  day  to  day,  it  is  only  necessary  to  determine  the 
carbon  dioxide  of  the  expired  air  and  the  carbon  and  nitrogen 
of  the  waste  products,  in  order  to  calculate  the  amounts  of 
material  oxidized  and  of  energy  liberated  in  the  body.  Ex- 
periments of  this  sort  have  played  a  most  important  part  in 
the  development  of  our  knowledge  of  nutrition.  The  cal- 
culations are  usually  based  on  the  following  average  analyses 
of  protein  and  body  fat :  — 


Carbon    . 
Nitrogen 
Hydrogen 
Oxygen    . 
Sulphur   . 


140 


CHEMISTRY    OF    FOOD    AND   NUTRITION 


The  following  data  were  obtained  with  a  man  on  ordinary 
mixed  diet :  — 

Calculation  of  Energy  Metabolism  from  Carbon  and  Nitrogen 
Balance.  Man  of  64  Kilograms  at  Rest  in  Atwater  Respiration 
Apparatus 


Grams  per  Day 

Protein 

Fat 

Carbohy- 
drate 

Nitrogen 

Carbon 

Total  in  food     . 
Lost  in  digestion 
Absorbed .     .     . 

94.4 

5-4 

89.0 

82.5 

3-7 

79.8 

289.8 

3-2 

286.6 

15.1 

0.9 

14.2 

16.2 

16.2 

—  2.0 

239.0 

7-4 

231.6 

Output 

By  lungs 

207.3 
12  2 

By  kidneys 

Metabolized 

219.5 

4-  12  I 

Balance        .... 

A  loss  of  2.0  grams  body  nitrogen  indicates  (2.0  X  6.25  =) 
12.5  grams  body  protein  burned.  Also  there  were  89.0 
grams  absorbed  from  food,  and,  therefore,  in  all  101.5  grams 
total  protein  burned. 

Since  the  respiratory  quotient  showed  that  the' body  was 
in  carbohydrate  equilibrium  at  the  beginning  and  end  of 
each  experimental  day,  i.e.  at  seven  o'clock  each  morning,  it 
may  be  concluded  that  the  amount  of  carbohydrate  burned 
was  the  same  as  that  absorbed  from  the  food,  viz.  286.6 
grams  per  day. 


THE  FUEL  VALUE  OF  FOOD  141 

From  the  carbon  balance,  therefore,  we  estimate  the 
amount  of  fat  burned  as  follows :  — 

12.5  grams  body  protein  yield  (12.5  X  53  per 

cent  =) 6.6  grams  carbon 

And  there  were  in  the  absorbed  food    .     .     .  231.6  grams  carbon 

.'.  total  available  was 238.2  grams  carbon 

But  total  katabolized  was  only 219.5  grams  carbon 

.*.  the  body  stored  in  the  form  of  fat    .     .     .  18.7  grams  carbon 

Since  fat  contains  76.5  per  cent  carbon,  i  gram  carbon  =0  1.307 
grams  fat.     .'.  18.7  grams  carbon  =  24.4  grams  fat. 

The  body  therefore  absorbed  78.8  grams  fat 
stored  24.4  grams  fat 
burned     54.4  grams  fat 

In  all,  the  body  burned  per  day  — 

101.5  grams  protein,  yielding         (101.5  X  4.35  ^  =)    442  calories 
54.4  grams  fat,  yielding  (54.4  x  9.45  ^  =)    5i5  calories 

286.6  grams  carbohydrate,  yield- 
ing (286.6  X  4.1    ^  =)  1 1 75  calories 

2132  calories 

Sonden  and  Tigerstedt  studied  by  means  of  the  carbon 
and  nitrogen  balance  the  energy  metabolism  of  eight  resting 
men  between  nineteen  and  forty-four  years  of  age,  with  results 
which  varied  for  the  different  subjects  from  1853  to  2292  calo- 
ries per  day.  Many  experiments  by  other  workers  might 
be  cited  in  confirmation  of  this  result. 

^  Here  the  factors  for  fuel  value  are  not  reduced  to  allow  for  loss  in 
digestion,  because  this  loss  has  already  been  deducted  in  computing  the 
amount  of  each  nutrient  actually  absorbed  and  rendered  available. 


142  CHEMISTRY    OF    FOOD    AND    NUTRITION 

Calorimeter  Experiments.  —  Although  several  forms  of 
apparatus  have  been  employed  to  measure  the  output  of 
heat  from  the  human  body,  it  was  not  until  the  development 
of  the  Atwater-Rosa-Benedict  respiration  calorimeter  that 
complete  and  satisfactory  data  covering  periods  of  one  to 
several  days  had  been  obtained.  This  apparatus  consists 
of  an  air-tight  copper  chamber,  surrounded  by  zinc  and 
wooden  walls  with  air-spaces  between,  and  is  large  enough 
for  a  man  to  live  in  without  discomfort,  being  about  7  feet 
long,  4  feet  wide,  and  6\  feet  high.  An  opening  in  the  front 
of  the  apparatus,  which  is  sealed  during  an  experiment, 
serves  as  both  door  and  window  and  admits  sufficient  light  for 
reading  and  writing.  A  smaller  opening  in  the  rear  wall, 
ha\'ing  tightly  fitting  caps  on  both  ends,  is  used  for  passing 
food,  drink,  excreta,  etc.,  into  and  out  of  the  chamber.  The 
chamber  is  furnished  with  a  folding  bed,  chair,  and  table, 
and  is  ventilated  by  means  of  a  current  of  air  which  passes 
usually  at  the  rate  of  about  2^  cubic  feet  per  minute.  At 
first  this  ventilating  air  current  was  maintained  and  meas- 
ured by  means  of  a  specially  constructed  meter  pump  which 
also  automatically  took  samples  of  the  air  for  analysis.  Re- 
cently the  apparatus  has  been  so  modified  as  to  make  use 
of  the  same  air  throughout  an  experiment,  the  carbon  di- 
oxide and  water  given  off  by  the  subject  being  removed  by 
circulating  the  air  through  purifying  vessels,  and  the  oxygen 
which  the  subject  uses  being  replaced  by  adding  weighed 
amounts  of  oxygen  to  the  air  current  as  required.     By  this 


THE  FUEL  VALUE  OF  FOOD  I43 

means  it  is  possible  to  carry  out,  in  the  calorimeter,  metabo- 
lism experiments  in  which  the  oxygen  and  hydrogen  as  well 
as  the  carbon  and  nitrogen  balances  are  determined,  and 
from  these  data  the  gain  or  loss  of  carbohydrate  as  well  as  of 
protein  and  fat  can  be  determined. 

The  ventilating  air  current  is  so  regulated  that  it  enters 
and  leaves  the  calorimeter  at  the  same  temperature;  and 
between  the  copper  and  zinc  walls  are  placed  a  large  number 
of  thermoelectric  junctions  connected  with  a  delicate  gal- 
vanometer by  means  of  which  each  wall  is  tested  every 
four  minutes,  day  and  night,  during  the  progress  of  an  ex- 
periment, and  the  minute  amounts  of  heat  which  may  pass 
to  or  from  the  calorimeter  through  its  walls  are  quickly  de- 
tected and  made  to  balance  each  other.  Thus  there  is  no 
gain  or  loss  of  heat  either  through  the  walls  of  the  chamber 
or  by  the  ventilating  air  current,  and  the  heat  given  off  by 
the  subject  can  leave  only  by  the  means  especially  provided 
for  carrying  it  out  and  measuring  it.  A  part  of  the  heat 
liberated  is  carried  from  the  chamber  in  latent  form  by  the 
water  vapor  in  the  outgoing  air,  which  is  accurately  deter- 
mined. The  rest  of  the  heat  is  brought  away  by  means  of 
a  current  of  cold  water  circulating  through  a  copper  pipe 
coiled  near  the  ceiling  of  the  chamber.  The  quantity  of 
water  which  passes  through  the  pipe  and  the  difference 
between  the  temperature  at  which  it  enters  and  that  at 
which  it  leaves  the  coil  are  carefully  determined  and  show 
how  much  heat  is  thus  brought  out  of  the  chamber. 


144  CHEMISTRY    OF    FOOD    AND    NUTRITION 

By  means  of  this  apparatus,  for  an  adequate  description 
of  which  reference  must  be  made  to  the  pubUcations  of  At- 
water  and  Benedict/  it  is  possible  to  measure  the  heat  pro- 
duction or  energy  metaboUsm  of  a  man  for  a  period  of  a  day, 
or  of  several  days,  with  a  much  greater  degree  of  accuracy 
than  was  possible  by  the  earlier  methods.  The  discrepancy 
between  the  theoretical  heat  and  that  actually  measured 
by  this  apparatus  rarely  reaches  2  per  cent  in  any  single  ex- 
periment, while  in  the  average  of  45  experiments  covering 
143  experimental  days  the  theoretical  heat  was  to  the  heat 
actually  measured  as  10,000  to  9999.  The  results  obtained 
by  this  method  of  experimenting  are  more  convincing  than 
those  reached  in  any  other  way. 

At  the  time  of  writing  there  are  available  the  completed 
data  of  experiments  upon  6  different  men  w^ho  lived  in  the 
calorimeter  at  comparative  rest,  taking  as  a  rule  but  little 
more  exercise  than  was  involved  in  dressing  and  undressing, 
folding  and  unfolding  the  bed,  table,  and  chair,  taking  samples 
and  observations  pertaining  to  the  experiment,  writing,  etc., 
in  short,  the  life  of  a  healthy  man,  confined  to  one  small 
room. 

The  average  daily  metabolism  of  each  of  the  subjects  was 
as  in  the  following  table. 

^  Publication  No.  42,  Carnegie  Institution  of  Washington,  and  Bul- 
letins of  the  Office  of  Experiment  Stations,  U.  S.  Dept.  of  Agriculture. 


THE    FUEL    VALUE    OF    FOOD 


145 


Subject 

Age 
Years 

Weight 
Average 

Number  of 
Experi- 
ments 

Total  Ex- 
perimental 
Days 

Calories 
PER  Day 

E.O 

A.  W.  S.  .     .     . 
J.  F.  S.     .     .     . 
J.  C.  W.  .     .     . 
H.  F 

B.  F.  D.  .    .     . 

Mean  of  individ- 
ual averages 

31-34 
22-25 

29 
21 

54 
23 

70  K. 

(154  lb.) 
70  K. 

(154  lb.) 
65  K. 

(143  lb.) 
76  K. 

(168  lb.) 
70  K. 

(154  lb.) 
67  K. 

(147  lb.) 

13 
4 

4 

I 
I 
I 

42 

9 

12 

4 
3 
3 

2283 
2337 
2133 
2397 
1904 
2228 

2213 

Extreme  deviations  from  the  mean,  +  184  to  —  309  calories, 

or  +  8.4  to  —  14  per  cent. 

Omitting  the  results  obtained  with  the  one  subject  who 
was  considerably  older  than  the  others,  the  figures  become  as 
follows :  — 

Mean  of  individual  averages,       2277  calories. 
Extreme  deviations  from  mean,  +  120  to  —  144  calories, 

or  +  5.2   to  —  6.3  per  cent. 
Deviations  in  body  weight,  +  8.7  to  —  7.1  per  cent. 

The  subject  "H.  F.,"  aged  fifty-four,  who  for  a  number  of 
years  had  practiced  a  very  restricted  diet  and  believed  that 
he  consumed  only  half  the  usual  amount  of  food,  had  a  food 


146  CHEMISTRY    OF   FOOD    AND   NUTRITION 

requirement  about  15  per  cent  less  than  that  of  the  younger 
men  averaging  about  the  same  weight.  That  several  years' 
effort  to  Uve  upon  a  diminished  amount  of  food  should  have 
resulted  in  no  greater  change  than  might  have  been  due  to 
his  age  alone  is  striking  evidence  of  the  fixed  character  of 
the  food  requirement.  The  five  younger  men  varied  in  age 
from  twenty-one  to  thirty-four  years,  were  natives  of  three 
different  countries,  and  had  been  accustomed  to  very  dif- 
ferent dietary  habits  and  modes  of  Ufe,  yet  they  differed 
less  in  food  requirements  than  in  body  weight. 

[Since  the  above  was  written  Benedict  and  Carpenter 
have  published  data  for  other  men  who  differed  more  in 
age  and  physique  and  showed  somewhat  larger  individual 
differences  in  metabolism.] 

Equally  interesting  is  the  close  agreement  between  these 
results  and  those  reached  by  the  methods  previously  de- 
scribed. A  general  view  of  the  results  obtained  by  all  four 
of  the  methods  leads  to  the  conclusion  that  the  food  require- 
ments of  a  young  to  middle-aged  man  of  average  size,  kept 
strictly  at  rest,  approximates  2000  calories  per  day,  and  that 
such  muscular  activity  as  is  incidental  to  very  quiet  Uving 
indoors  may  be  expected  to  raise  this  requirement  to  2200 
or  2300  calories  per  day.  The  very  close  agreement  in  results 
reached  by  many  independent  investigators,  using  four 
distinct  methods  of  study,  must  be  taken  as  establishing  the 
approximate  average  food  requirement  of  a  man  at  rest 
beyond  any  reasonable  doubt. 


THE  FUEL  VALUE  OF  FOOD  I47 

Next  will  be  considered  the  principal  conditions  which 
influence  the  total  metabolism  and  food  requirement. 

REFERENCES 

Armsby.     Principles  of  Animal  Nutrition,  Chapters  7  to  10. 
Atwater.     Methods  and  Results  of  Investigations  on  the  Chemistry  and 

Economy  of  Food.     Bull.  21,  Office  of  Experiment  Stations,  U.  S. 

Dept.  Agriculture  (1895). 
— —  Neue  Versuche  ueber  Stoflf-  und  Kraft-wechsel.     Ergebnisse  der 

Physiologie,  3  (1904). 
Atwater  and  Benedict.     A  Respiration  Calorimeter  with  Appliances 

for   the   Direct   Determination   of   Oxygen.     Publication   No.   42, 

Carnegie  Institution  of  Washington  (1905). 
Benedict  and  Carpenter.     The  Metabolism  and  Energy  Transforma- 
tions of  Healthy  Man  During  Rest.     Publication  No.  1 26,  Carnegie 

Institution  of  Washington  (1910). 
Fisher.     A  new  method  for  indicating  Food  Values.    American  Journal 

of  Physiology,  15,417. 
LusK.     Elements  of  the  Science  of  Nutrition,  2d.  ed.  pp.  17-45  (1909). 
Nagel.     Handbuch  der  Physiologie  des  Menschen,  pp.  331-375  (1909). 
Oppenheimer.     Handbuch  der  Biochemie,  4,  II,  1-92. 
Tigerstedt.     Textbook  of  Physiology,  Chapter  4  (1906). 
RuBNER.     Der  Energiewert  der  Kost  des  Mencshen.     Zeitschrijt  Jiir 

Biologic  (n.f.),  24,  261-308  (1901). 

Die  Gesetze  der  Energieverbrauches  bei  der  Ernahrung  (1902). 

VoN  Noorden.     Metabolism  and  Practical  Medicine,  Vol.  I,  pp.  185- 

207. 


CHAPTER    VI 

CONDITIONS    AFFECTING    THE   TOTAL    FOOD 
REQUIREMENT 

Activity,  age,  and  size  are  the  most  important  factors  in- 
fluencing the  total  food  requirement  of  the  body.  The  food 
requirement  of  the  adult  being  more  accurately  known  than 
that  of  the  growing  organism,  it  will  be  convenient  to  con- 
sider the  demands  of  work,  and  of  other  conditions  affecting 
the  adult  first,  and  those  of  growth  later. 

The  muscular  movements  of  the  body  have  for  their 
object  the  performance  of  work  of  three  kinds  :  — 

1.  The  work  of  the  voluntary  muscles,  including  all  of 
the  "external  work"  in  the  sense  in  which  the  term  is  or- 
dinarily used. 

2.  The  work  of  digestion  and  assimilation,  which,  once 
the  food  is  swallowed,  is  involuntary,  but  which  is  external 
in  the  sense  of  being  done  upon  material  which  is  not  yet 
a  part  of  the  body. 

3.  The  work  which  goes  on  in  the  body  independently 
of  either  of  these,  and  which  is  internal  in  a  strict  physiologi- 
cal sense  —  such,  for  example,  as  the  work  of  the  circula- 
tion and  of  the  maintenance  of  muscular  elasticity. 

Experimentally  it  is  possible  to  control  the  work  of  the 
first  and  second  kinds;  but  the  true  internal  work  cannot 

148 


CONDITIONS   AFFECTING   FOOD    REQUIREMENT       149 

be  stopped  during  the  life  of  the  animal  and  in  some  cases 
cannot  be  greatly  modified,  except  by  radical  departure 
from  normal  conditions.  Attempts  to  differentiate  quanti- 
tatively between  the  different  kinds  of  internal  work  are 
therefore  attended  with  much  difficulty.  The  maintenance 
requirement  in  the  sense  in  which  the  term  has  been  used 
here  covers  the  work  of  digestion  and  assimilation  as  well 
as  the  true  internal  work,  but  excludes  as  far  as  practicable 
the  external  work  of  the  voluntary  muscles. 

A  systematic  analysis  of  the  maintenance  requirement 
of  the  body  with  reference  to  its  principal  functions  has  not 
yet  been  made,  but  results  obtained  by  Armsby,  Atwater, 
Benedict,  ^lagnus-Levy,  Rubner,  Zuntz,  and  others  indicate 
that  about 

8-1 2  per  cent  of  the  maintenance  requirement  of  energy  is  ex- 
pended upon  the  work  of  digestion  and  assimilation, 
including  any  direct  response  of  the  body  to  the  food 
(specific  dynamic  effect), 
5-10  per  cent  upon  the  circulation, 
10-20  per  cent  upon  the  respiration, 

30-50  per  cent  upon  the  maintenance  of  muscular  tension,  elas- 
ticity, or  "tone," 
?  per  cent  upon  the  work  of  the  secreting  cells  other  than 
those  of  digestion  and  other  forms  of  intracellular 
work. 

These  estimates,  while  not  final,  are  helpful  in  considering 

the  influence  of  food  consumption,  muscular  activity,  and 

other  factors  upon  the  energy  metabolism  and  the  resulting 

food  requirement. 


150  CHEMISTRY    OF    FOOD    AND    NUTRITION 

INFLUENCE    OF    FOOD    CONSUMPTION    UPON 
METABOLISM 

Comparison  of  Feeding  and  Fasting  Experiments.  —  The 
direct  effect  of  the  consumption  of  food  upon  the  general 
metabolism  is  most  conveniently  observed  by  means  of  the 
Zuntz  respiration  apparatus  already  mentioned,  because 
of  the  ease  with  which  changes  occurring  in  short  periods 
can  be  measured  by  means  of  this  apparatus.  Using  this 
method,  Magnus-Levy,  by  determining  the  oxygen  consump- 
tion per  hour  throughout  the  daytime,  found  that  this  was 
23  to  40  per  cent  higher  during  the  first  two  hours  after 
meals  than  while  fasting  early  in  the  morning.  The  rate  of 
metabolism  had  returned  to  the  early  morning  value  within 
4-5  hours  after  breakfast  and  supper  and  within  6-7  hours 
after  a  noon  dinner.  The  total  food  taken  furnished  2400 
to  2500  calories,  and  the  increased  metabolism  in  the  hours 
following  meals  amounted  in  all  to  190  to  200  calories,  or 
about  8  per  cent  of  the  energy  furnished  by  the  food. 

At  water  and  Benedict  determined  directly  by  means  of 
the  respiration  calorimeter  the  heat  production  of  the  same 
man  during  five  fasting  experiments  of  one  to  two  days  each, 
and  during  a  four-day  experiment  with  food  about  sufficient 
for  maintenance.  The  average  total  metabolism  on  the 
fasting  days  was  about  9  per  cent  lower  than  on  the  days 
when  food  was  taken. 

In  a  more  recent  series  of  experiments  Benedict  has  found 
that,  if  the  fast  is  sufficiently  prolonged,  there  may  be  a  some- 


CONDITIONS    AFFECTING    FOOD    REQUIREMENT       151 


what  greater  decrease  in  heat  production.  Thus,  a  man 
who  weighed  at  the  start  59.5  kilograms  (131  pounds), 
metabolized  on  the  successive  days  of  a  seven-day  fast,  1765, 
1768,  1797,  1775,  1649,  1553,  and  1568  calories  respectively. 
Naturally  in  such  a  long  fast  other  factors  than  the  simple 
sparing  of  the  work  of  digestion  come  into  play. 

Tigerstedt  has  studied  by  means  of  the  carbon  and  nitro- 
gen balance  the  metabolism  of  a  man  who  fasted  for  five 
days  and  for  the  next  two  days  took  a  very  liberal  diet.  The 
heat  production  for  the  first  two  days  of  fasting  could  not 
be  estimated  so  accurately  as  for  the  other  days,  since  at  this 
time  the  body  was  losing  an  unknown  amount  of  glycogen. 
The  following  data  were  obtained :  — 


ist  fast  day 

2d  fast  day 

3d  fast  day 

4th  fast  day 

5th  fast  day  .  .  .  .  . 
Fed  4141  calories  .  .  . 
Fed  4141  calories  (2d  day) 


Body  Weight 
Kilos 


67.0 

65.7 
64.9 
64.0 

63.1 
64.0 
65.6 


Calculated 

Total 

Metabolism 

Calories 


2220  ^ 
2102  ^ 
2024 
1992 
1970 

2437 
2410 


Calories  per 
Kilo 


33-2^ 
32.0  1 
31.2 

3I-I 
31.2 

38.1 
36.8 


These  results  show  for  man  (as  had  previously  been  shown 
with  dogs)  that  in  fasting  the  total  metabolism  continues 

1  These  figures  are  slightly  too  high  because  the  loss  of  carbon  on  these 
days  was  due  in  part  to  combustion  of  glycogen,  but  is  calculated  as  if 
due  simply  to  protein  and  fat. 


152  CHEMISTRY    OF   FOOD   AND    NUTRITION 

at  a  fairly  constant  rate  in  spite  of  the  fact  that  the  energy 
is  obtained  entirely  at  the  expense  of  body  material.  In 
this  case,  the  diet  given  at  the  end  of  the  fasting  period 
(4141  calories)  was  approximately  double  what  would  have 
been  required  for  maintenance,  thus  making  the  work  of 
digestion  and  assimilation  presumably  twice  as  great  as  when 
a  maintenance  diet  is  taken.  The  observed  increase  of  me- 
taboUsm  (22.5  per  cent)  is  therefore  little,  if  any,  greater 
than  could  be  explained  by  the  work  of  digestion  and  assimila- 
tion alone,  the  balance  of  the  increase  (if  any)  being  prob- 
ably due  to  the  internal  work  involved  in  the  regrowth 
of  the  tissues,  since  during  these  two  days  the  body  regained 
20  per  cent  of  the  protein,  36  per  cent  of  the  fat,  71  per  cent 
of  the  water,  and  69  per  cent  of  the  ash  which  it  had  lost 
during  the  five  days  of  fasting. 

The  results  of  fasting  exp>eriments  thus  make  it  evident 
that  the  total  metabolism  of  any  given  man  at  rest  tends  to 
remain  fairly  constant,  and  that  the  body  has  but  little  power 
in  the  direction  of  adjusting  its  energy  metabolism  to  its 
food  supply. 

Specific  Dynamic  Action  of  the  Foodstuffs.  —  Rubner  found 
that  each  type  of  food  exerted  a  more  or  less  specific  influ- 
ence upon  the  energy  metabolism,  so  that  when  the  foodstuffs 
were  fed  separately,  somewhat  different  energy  values  were 
required  for  the  maintenance  of  body  equilibrium.  Thus,  if 
the  total  metabolism  of  a  dog  fasting  at  33°  C.  be  represented 
by  100  calories,  he  must  be  fed,  in  order  to  prevent  loss  of 


CONDITIONS   AFFECTING   FOOD   REQUIREMENT       1 53 

body  substance,  about  106.5  calories  of  sugar,  or  114.5  calories 
of  fat,  or  140  calories  of  protein.  A  man  observed  by  Rub- 
ner  metabolized  in  fasting  2042  calories;  when  fed  2450 
calories  in  the  form  of  sugar  alone,  he  metabolized  2087 
calories;  when  fed  2450  calories  in  the  form  of  meat  alone, 
he  metabolized  2566  calories.  It  is  not  yet  clear  why  the 
eating  of  protein  should  increase  the  metabolism  so  much 
more  than  does  the  eating  of  the  same  number  of  calories 
in  the  form  of  carbohydrate  and  fat.  It*  would  seem  that 
there  is  in  any  case  a  certain  reaction  of  the  body  to  the  food 
which  it  receives,  which  may  perhaps  be  due  to  the  work  of 
digestion  and  assimilation,  but  that  in  the  case  of  protein 
there  is  an  additional  specific  stimulation  due  to  the  nature 
of  the  foodstuff  or  the  products  of  its  metabolism.  What- 
ever the  cause  of  this  specific  dynamic  action  of  protein,  it 
is  at  present  believed  that  there  is  here  involved  a  liberation 
of  energy  which  has  not  come  into  the  service  of  the  tissues 
and  which  does  not  directly  contribute  to  the  support  of 
their  activities,  though  it  may  aid  in  the  maintenance  of  body 
temperature.  On  an  ordinary  mixed  diet,  however,  this 
apparent  loss  of  a  part  of  the  fuel  value  of  protein  is  not  a 
very  important  factor  in  the  total  metabolism,  since  this 
specific  dynamic  action  and  the  work  of  digestion  and  assimi- 
lation together  make  the  total  daily  metabolism  of  energy 
only  about  one  tenth  higher  on  a  maintenance  ration  than 
when  no  food  is  eaten. 


154  CHEMISTRY    OF    FOOD    AND    NUTRITION 

INFLUENCE    OF    MUSCULAR   WORK    UPON   METABO- 
LISM  AND   FOOD   REQUIREMENTS 

Muscular  work  is  much  the  most  important  of  the  fac- 
tors which  raise  the  food  requirements  of  adults  above  the 
2  GOO  calories  (or  thereabouts)  necessary  for  maintenance  at 
rest. 

Accurate  measurements  by  means  of  the  calorimeter  have 
shown  that  the  average  total  metabolism  of  a  man  sitting 
still  is  about  loo  calories  per  hour;  wMe  the  same  man 
working  actively  increases  his  metabolism  up  to  about  300 
calories  per  hour;  and  a  well-trained  man  working  at  about 
his  maximum  capacity  metabolizes  material  enough  to  Hberate 
600  calories  per  hour,  i.e.  his  metabolism  may  be  six  times 
as  active  during  the  hours  actually  spent  in  such  work  as 
when  he  is  at  rest.  If  during  24  hours  a  man  works  as  hard 
as  this  for  8  hours  and  spends  2  hours  in  such  light  exercise 
as  going  to  and  from  work,  his  food  requirement  for  the  day 
will  be  somewhat  over  6000  calories,  or  three  times  the 
maintenance  requirement.  Thus,  work  may  increase  the 
day's  metabolism  as  much  as  200  per  cent,  whereas  we  saw 
that  liberal  feeding  at  the  end  of  a  fast  increased  the  me- 
tabolism only  22.5  per  cent,  or  one  ninth  as  much.  Only 
a  few  exceptional  occupations,  such  as  that  of  lumbermen, 
for  example,  involve  such  heavy  work  as  to  cause  a  metab- 
oUsm  of  6000  calories  per  day.  More  often  the  man  who 
works  eight  hours  a  day  at  manual  labor  will  increase  his 
metaboUsm  by  1000  to  2000  calories  above  what  is  needed 


CONDITIONS    AFFECTING   FOOD    REQUIREMENT        1 55 

for  maintenance  at  rest,  making  his  total  food  requirement 
3000  to  4000  calories. 

Voit  estimated  the  food  requirement  of  a  "moderate 
worker"  al  about  3050  calories;  and  Atwater,  in  adapting 
this  standard  to  American  conditions,  increased  the  allow- 
ance to  3400-3500  calories  in  the  belief  that  the  American 
works  more  rapidly  and  therefore  with  a  greater  expenditure 
of  energy.  The  mistake  is  often  made  of  supposing  that 
these  estimates  were  intended  for  every  one  who  leads  an 
active  life,  whereas  they  really  contemplate  a  long  day  of 
manual  labor,  for  Voit's  definition  of  "moderate  worker" 
was  a  man  laboring  9  or  10  hours  a  day  at  an  occupation 
such  as  that  of  a  carpenter,  mason,  or  joiner. 

Quantitative  Relation  between  Work  performed  and  Total 
Metabolism.  —  Theoretically  it  is  possible  to  determine  the 
mechanical  efficiency  of  a  man  by  dividing  the  mechanical 
effect  of  his  work  by  the  increase  of  energy  metabolism 
which  the  work  involves.  This  gives  the  basis  on  which  to 
ascertain  how  much  extra  food  would  be  necessary  to  supply 
the  energy  required  for  the  performance  of  any  given  task. 
In  practice  it  is  extremely  difficult  to  measure  the  efficiency 
or  even  the  exact  mechanical  value  of  the  muscular  work 
performed. 

Since  increased  muscular  work  involves  a  simultaneous 
increase  of  oxidation  in  the  body,  and  the  carbon  dioxide 
which  is  the  principal  oxidation  product,  escapes  very  rapidly 
through  the  lungs,  the  immediate  influence  of  work  upon 


156 


CHEMISTRY    OF   FOOD    AND    NUTRITION 


metabolism  is  most  conveniently  shown  by  respiration  ex- 
periments in  which  the  periods  of  observation  can  be  reduced 
to  cover  only  the  time  of  actual  muscular  effort.  Experi- 
ments of  this  kind  (made  especially  by  use  of  the  Zuntz 
apparatus  already  described)  are  discussed  at  some  length 
by  Magnus-Levy  in  Von  Noorden's  Metabolism  and  Practi- 
cal Medicine,  and  some  of  the  deductions  drawn  from  them 
may  be  summarized  as  follows :  — 

The  amount  of  oxygen  consimied  during  work  in  excess  of  that 
during  rest  was  regarded  as  a  measure  of  that  expended  upon  the 
work.  As  a  rule  the  increased  consumption  of  oxygen  during 
work  is  relatively  greater  than  the  increased  volume  of  air  breathed, 
so  that  a  greater  proportion  of  the  oxygen  of  the  inspired  air  must 
be  taken  up  by  the  lungs.  As  an  example  of  the  increase  of  oxy- 
gen consumption  with  muscular  work  the  data  obtained  by  Katz- 
enstein  in  experiments  upon  the  work  of  walking  up  an  inclined 
plane  may  be  given.     The  figures  were  as  follows :  — 


Oxygen 

CONSUMED 

PER  Minute 

Respira- 
tory 
Quotient 

Horizontal 
Distance 

Ascent 

At  rest 

Walking  on  very  slight  incline 

Walking  up  incline  with  10.8 

per  cent  rise 

cc. 
263.75 
763.00 

1253-2 

0.801 

0.805 

0.801 

Meters 
74.48 
67.42 

Meters 
0.58 
7.27 

The  constancy  of  the  respiratory  quotient  indicates  that  here 
there  was  no  change  in  the  nature  of  the  material  burned  in  the 
body  on  passing  from  rest  to  gentle,  or  from  gentle  to  active 


CONDITIONS   AFFECTING   FOOD   REQUIREMENT       1 57 

exercise.  The  greatly  increased  work  did  not  lead  to  the  burning 
of  any  one  nutrient  in  preference  to  another. 

The  weight  moved  (that  of  the  subject  and  his  clothing)  was  in 
this  case  55.5  kilograms.  From  these  data  it  was  calculated  that 
a  consumption  of  energy  equivalent  to  0.223  kilogram-meters 
was  required  to  move  i  kilogram  of  weight  horizontally  over  a 
distance  of  i  meter;  and  2.924  kilogram-meters  of  energy  to  raise 
I  kilogram  through  a  vertical  distance  of  i  meter. 

Experiments  upon  several  other  subjects  gave  similar  results, 
indicating  that  these  men  who,  while  not  trained  in  an  athletic 
sense,  were  physically  sound  and  thoroughly  accustomed  to  this 
form  of  exercise,  were  able  to  perform  i  kilogram-meter  of  work 
in  the  ascent  of  the  incline  with  an  expenditure  of  only  about  3 
kilogram-meters  of  energy  over  that  required  at  rest,  so  that  the 
work  was  done  with  a  mechanical  efficiency  of  about  33  per  cent. 
It  is  to  be  noted,  however,  that  this  applies  only  to  walking  done 
under  the  most  favorable  conditions,  and  not  carried  to  the  point 
of  fatigue;  also  that  robust  men  unaccustomed  to  this  form  of 
exercise  showed  only  two  thirds  to  three  fourths  as  high  an  effi- 
ciency until  after  several  days'  practice.  The  energy  expended 
in  forward  progression  was  about  one  thirteenth  of  that  required 
to  raise  the  body  through  the  same  distance. 

On  this  basis  it  might  be  estimated  that  a  man  of  average 
weight  in  walking  one  mile  on  level  ground  would  do  8000- 
9000  kilogram-meters  of  work,  or  about  the  mechanical 
equivalent  of  20  calories.  If  this  were  accomplished  with 
an  efficiency  of  33  per  cent,  it  would  involve  an  expenditure 
of  only  60  calories,  but  at  an  efficiency  of  20  per  cent  100 
calories  per  mile  would  be  required.  These  figures,  while 
only  approximate,  may  be  helpful  in  estimating  the  food 
requirements  of  men  who  neither  do  active  physical  labor 


158  CHEMISTRY    OF    FOOD    AND    NUTRITION 

nor  take  vigorous  exercise,  yet  move  about  more  freely  than 
in  the  so-called  rest  experiments  already  described.  If, 
for  example,  it  be  assumed  that  a  healthy  man  would  require 
2200  calories  per  day  when  remaining  in  one  room,  and  that 
the  total  additional  muscular  movements  of  a  day  at  business 
and  recreation  were  equivalent  to  walking  five  miles  on 
level  ground,  his  total  food  requirement  for  the  day  would 
become  2500  to  2700  calories  (36  to  39  calories  per  kilogram), 
while  activity  equivalent  to  walking  ten  miles  on  level 
groimd  would  bring  the  total  daily  requirements  to  2800  to 
3200  calories  (40  to  46  calories  per  kilogram). 

By  means  of  the  respiration  calorimeter,  Atwater  and 
Benedict  have  studied  the  question  of  mechanical  efficiency 
with  more  accurate  measurements  of  the  energy  involved 
than  in  the  experiments  with  the  Zuntz  apparatus,  but  with 
a  less  favorable  form  of  muscular  work.  For  work  experi- 
ments there  is  placed  in  the  calorimeter  chamber  an  ergom- 
eter,  which  consists  of  a  fixed  bicycle  frame  having  in  place 
of  the  rear  wheel  a  metal  disc  which  is  revolved  against  a 
measured  amount  of  electrical  resistance,  so  that  the  me- 
chanical effect  of  the  muscular  work  is  very  accurately 
determined.  The  expenditure  of  energy  involved  in  the 
performance  of  this  work  is  estimated  by  comparing  the  total 
metabolism  of  a  working  day  with  that  of  the  same  man  when 
living  in  the  calorimeter  chamber  at  rest.  The  average 
results  obtained  with  three  different  men  were  as  fol- 
lows :  — 


CONDITIONS    AFFECTING    FOOD    REQUIREMENT        1 59 


StJBjECT  AND  Nature  of 
ExpERIME^^: 


Subject  E.  O. 

Average    13   rest   experiments    (42 

days)       

Average   3    work   experiments    (12 

days) .     . 

Subject  J.  F.  S. 

Average    4    rest    experiments    (12 

days)        

Average   6   work   experiments    (18 

days)        

Subject  J.  C.  W. 

Average  i  rest  experiment  (4  days)  . 

Average  14  work  experiments  (46 

days)        


Energy 

TRANSFORMED 

Heat 

Equiv.  of 

Work 

PER- 
FORMED 

Total  per 
day 

Excess 

over  that 

at  rest 

calories 

calories 

calories 

2279 

3892 

1613 

214 

2119 

3559 

1440 

233 

2357 

5143 

2786 

546 

Mechan- 
ical Ef- 
ficiency 


per  cent 


13-3 


16.2 


19.6 


That  the  efFiciency  here  shown  is  inferior  to  that  found  by 
the  Zuntz  method  is  probably  due  to  a  number  of  causes. 
The  work  upon  the  ergometer  would  naturally  be  less  familiar 
and  therefore  less  economically  done  than  that  of  walking. 
Experiments  of  three  or  four  days'  duration  (as  in  the  calo- 
rimeter) are  not  long  enough  to  ensure  a  maximum  of  train- 
ing; while  on  the  other  hand,  the  working  time  of  each  day 
and  the  rate  at  which  the  subject  worked  on  the  ergometer 
were  probably  both  in  excess  of  what  would  show  the  highest 
percentage  efficiency.  Four  hours  of  work  in  the  morning  and 
four  in  the  afternoon  was  usual  on  working  days  in  the  calo- 


l6o  CHEMISTRY    OF    FOOD    AND    NUTRITION 

rimeter  experiments,  in  which  for  other  reasons  it  was  desired 
that  the  work  be  made  about  as  active  as  the  subject  could 
perform  without  undue  fatigue.  Leo  Zuntz  has,  however, 
shown  that  during  such  a  ride  there  is  a  marked  decUne  of 
efficiency.  WTien  he  cycled  for  four  successive  hours  at  an 
average  rate  of  15  to  17  kilometers  (about  9  miles)  per  hour, 
he  experienced  no  feeling  of  fatigue ;  but  his  determinations 
showed  that  the  expenditure  of  energy  necessary  to  produce 
a  given  effect  had  increased  about  9,  13,  10,  and  23  per  cent 
at  the  end  of  i,  2,  3,  and  4  hours  respectively.  This  is  be- 
cause if  the  same  kind  of  work  be  performed  for  a  series  of 
hours,  auxiUary  muscles  are  gradually  brought  increasingly 
into  action,  partly  for  the  performance  of  the  work  itself, 
partly  for  the  fixation  of  the  bodily  framework.  These 
auxiliary  muscles  work  less  economically  than  those  which 
first  and  most  naturally  come  into  play.  For  the  same 
reasons  there  is  a  lower  efficiency  in  the  case  of  work  which 
is  from  the  first  of  too  fatiguing  a  nature  because  of  being 
either  excessive  or  unsuitably  distributed  over  the  muscular 
system.  Similarly  auxiliary  muscles  come  into  play,  and 
the  metabolism  therefore  increases  whenever  the  onset  of 
pain  enforces  a  restriction  in  the  action  of  the  muscles  at 
work.  In  one  case  the  metabolism  during  a  march  was  in- 
creased about  20  per  cent  in  consequence  of  an  inflammation 
of  the  foot.  A  steep  gradient  or  an  increase  in  the  rate  of 
work  lowers  the  efficiency.  Thus,  Leo  Zuntz  found  that 
increasing  his  speed  2.4  times  increased  the  metabolism  4.3 
times  (Magnus-Levy). 


CONDITIONS   AFFECTING   FOOD   REQUIREMENT       l6l 

These  considerations  explain  the  difference  in  efficiency 
found  in  the  two  series  of  investigations  above  cited,  and 
indicate  that  the  lower  figures  as  determined  by  Atwater  and 
Benedict  will  doubtless  more  nearly  represent  the  efficiency 
to  be  expected  in  ordinary  muscular  labor. 

In  practice,  it  is  usually  so  difficult  to  estimate  the  me- 
chanical equivalent  of  muscular  work  performed  that,  as  yet, 
it  is  still  often  necessary  to  make  use  of  such  indefinite  terms 
as  "active,"  "severe,"  etc.,  to  describe  the  intensity  of  the 
exertion  and  thus  indicate  in  a  general  way  the  amount  of 
work  done.  From  the  results  of  many  work  experiments  with 
vigorous  young  men  in  the  respiration  calorimeter,  Atwater 
and  Benedict  have  derived  the  following  estimates  of  the  aver- 
age rate  of  metabolism  under  different  conditions  of  activity. 

Man  sleeping 65  calories  per  hour. 

Man  sitting  at  rest 

Man  at  light  muscular  exercise     . 
Man  at  active  muscular  exercise 
Man  at  severe  muscular  exercise 
Man  at  very  severe  muscular  exercise 


100  calories  per  hour. 
170  calories  per  hour. 
290  calories  per  hour. 
450  calories  per  hour. 
600  calories  per  hour. 


By  the  use  of  these  estimates  the  probable  food  require- 
ment may  be  calculated  very  simply,  as,  for  instance,  in  the 
following  example :  — 

8  hours  of  sleep  at  65  calories  =    520  calories 

2  hours'  light  exercise  ^  at  170  calories  =    340  calories 

8  hours'  active  exercise  at  290  calories  =  2320  calories 

6  hours'  sitting  at  rest  at  100  calories  =    600  calories 

Total  food  requirement  for  the  day,  3780  calories 

^  Going  to  and  from  work,  for  example. 


1 62  CHEMISTRY   OF   FOOD    AND   NUTRITION 

If  the  eight  working  hours  be  spent  at  severe  muscular 
work,  the  day's  food  requirement  would  be  estimated  at  5060 
calories;  wMe,  on  the  other  hand,  if  they  were  exclusively 
spent  sitting  still  at  a  desk,  the  estimate  would  be  only  2260 
calories  per  day  (about  32  calories  per  kilogram). 

Tigerstedt,  in  his  Textbook  of  Physiology^  gives  estimates 
of  food  requirements  for  different  degrees  of  activity,  indicat- 
ing the  intensity  of  the  work  by  means  of  typical  occupations. 
According  to  Tigerstedt :  — 

2001-2400  calories  suffice  for  a  shoemaker. 
2401-2700  calories  suffice  for  a  weaver. 
2701-3200  calories  suffice  for  a  carpenter  or  mason. 
3  20 1 -4 1 00  calories  suffice  for  a  farm  laborer. 
4101-5000  calories  suffice  for  an  excavator. 
Over  5000  calories  suffice  for  a  lumberman. 

These  general  estimates  may  be  useful  in  checking  the 
results  obtained  by  means  of  the  factors  of  Atwater  and 
Benedict  given  above. 

Before  lea\'ing  the  subject  of  the  relation  of  muscular 
activity  to  metabolism,  it  may  be  well  to  point  out  that  the 
expenditure  of  energy  in  the  muscles  does  not  depend  simply 
upon  the  muscular  movements  performed,  but  also  to  a  con- 
siderable extent  upon  the  degree  of  tension,  or  tone,  main- 
tained in  the  muscle  while  it  is  apparently  at  rest.  That 
every  Uving  muscle  is  always  in  a  state  of  tension  is  ob\dous 
from  the  fact  that  it  gapes  open  if  cut.  It  is  equally  evident 
that  the  degree  of  tension  (and  therefore  the  expenditure  of 


CONDITIONS   AFFECTING   FOOD   REQUIREMENT       1 63 

energy  required  to  maintain  it)  varies  greatly  under  different 
conditions.  The  differences  observed  by  Atwater  and  Bene- 
dict between  the  metabolism  of  the  sleeping  hours  and  that 
of  the  hours  spent  sitting  up  without  muscular  movement 
(65  and  100  calories  respectively)  are  largely  due  to  the  more 
complete  relaxation  of  the  muscles  during  sleep.  Thus, 
there  is  in  the  resting  muscle  a  continual  expenditure  of 
energy  which  first  takes  the  form  of  muscular  tension,  or 
tone,  but  ultimately  appears  as  heat,  so  that  the  heat  pro- 
duction, or  energy  metabolism,  of  the  body  at  rest  depends 
to  a  considerable  extent  upon  the  degree  of  tension  which 
still  persists  in  the  muscles. 

THE   REGULATION   OF   TEMPERATURE 

The  influence  of  surrounding  temperature  upon  metabo- 
lism and  the  relation  of  metabolism  to  the  regulation  of  body 
temperature  are  fully  discussed  by  Lusk  in  his  Science  of 
Nutrition,  and  no  attempt  will  here  be  made  to  treat  the 
subject  systematically,  but  only  to  indicate  very  briefly 
the  more  important  bearings  upon  the  question  of  food  re- 
quirement. It  is  evident  that  the  maintenance  of  the  body 
at  a  temperature  above  that  of  its  ordinary  environment  in- 
volves a  continual  output  of  heat.  This  output  of  heat 
may  be  regulated  in  either  of  two  ways:  (i)  By  variations 
in  the  quantity  of  blood  brought  to  the  skin  which  tend 
to  control  the  loss  of  heat  by  radiation,  conduction,  and 
sweating;  this  is  called  the  physical  regulation.     (2)  By  an 


164  CHEMISTRY   OF   FOOD   AND    NUTRITION 

increase  in  the  rate  of  oxidation  in  the  body  in  response  to 
the  stimulus  of  external  cold;  such  a  change  in  the  rate  of 
oxidation  is  known  as  a  chemical  regulation.  The  extra 
heat  production  which  follows  the  taking  of  food  and  which 
has  been  mentioned  under  the  heading  of  the  specific  dynamic 
action  of  the  foodstuffs  may  take  the  place  of  the  "chemical 
regulation"  and  so  help  to  protect  the  body  from  the 
necessity  of  burning  material  simply  for  the  maintenance 
of  its  temperature.  The  presence  of  a  layer  of  adipose  tissue 
under  the  skin  as  well  as  the  custom  of  covering  the  greater 
part  of  the  external  surface  with  clothing  also  tends  to 
keep  down  the  loss  of  heat  to  the  point  where  "physical 
regulation"  will  sufl&ce.  Lusk  cites  experiments  by  Rubner 
upon  a  man  whose  metabolism  was  determined  w^hen  kept 
in  the  same  cold  room  but  with  different  amounts  of  clothing, 
and  observes  that  when  the  man  was  sufficiently  clothed  to 
be  comfortable  the  "chemical  regulation"  was  eUminated 
{Science  of  Nutrition^  2d  ed.,  p.  106). 

In  general  it  seems  probable  that  people  warmly  clothed 
and  living  (in  winter)  in  heated  houses  are  not  called  upon 
to  exercise  "chemical  regulation"  to  any  considerable  ex- 
tent; in  other  words,  they  probably  do  not  burn  any  con- 
siderable amount  of  material  merely  for  the  production  of 
heat,  the  heat  required  for  the  maintenance  of  body  tem- 
perature being  obtained  in  connection  with  the  metabolism 
which  is  essential  to  the  maintenance  of  the  muscular  ten- 
sion and  the  various  other  forms  of  internal  work.    If,  how- 


CONDITIONS   AFFECTING   FOOD   REQUIREMENT       1 65 

ever,  the  body  be  exposed  to  cold  it  may  be  forced  to  employ 
"chemical  regulation"  with  a  resulting  increase  of  the  food 
requirement,  and  this  will  occur  more  readily  in  a  thin  person 
than  in  one  who  is  well  protected  by  subcutaneous  fat. 

The  extra  heat  required  in  cold  weather  is  probably  ob- 
tained for  the  most  part  through  the  activities  of  the  muscles. 
It  is  a  matter  of  general  experience  that  one  instinctively 
exercises  the  muscles  more  vigorously  in  cold  weather  than 
in  warm,  and  if  one  attempts  to  endure  much  cold  without 
muscular  exercise  there  results  shivering  —  a  peculiar  in- 
voluntary form  of  muscular  activity  whose  function  appears 
to  be  to  increase  heat  production  through  increasing  the 
internal  work  of  the  body. 

To  a  large  extent  therefore  the  regulation  of  body  tem- 
perature, even  under  exposure  to  cold,  is  accomplished 
through  the  activity  and  tension  of  the  muscles,  the  relations 
of  which  to  metabolism  and  food  requirement  have  been 
considered  in  the  preceding  section. 

THE  INFLUENCE  OF  SIZE  AND  SHAPE  OF  THE  BODY 

For  different  adults  of  the  same  species  the  energy  me- 
tabolism and  therefore  the  total  food  requirement  as  a  rule 
increases  with  the  size,  but  not  to  the  same  extent  that  the 
body  weight  increases;  so  that  the  requirement,  though 
greater  in  absolute  amount,  is  less  per  unit  of  body  weight 
in  the  larger  individual  than  in  the  smaller.  The  energy 
metabolism  increases   in   proportion  to  the  surface  rather 


i66 


CHEMISTRY    OF   POOD    AND    NUTRITION 


than   the   weight.     Thus,    Rubner   collected   the   following 
data  from   experiments  upon  seven  different  dogs :  — 


No. 

Body  Weight 
Kilogram 

Heat  Production  in  Calories  per  Day 

Total 

Per  kilogram 

Per  square  meter 

I 

II 

III 

IV 

V 

VI 

VII 

3.10 
6.44 
9-51 
17.70 
19.20 
23.71 
30.66 

273.6 

417-3 
619.7 

817.7 

880.7 

970.0 

II  24.0 

88.25 
64.79 
65.16 
46.20 

45.87 
40.91 
36.66 

1214 
II 20 
I183 
1097 
1207 
III2 
1046 

Here  the  heat  production  in  calories  per  kilogram  was 
over  twice  as  great  in  the  smallest  as  in  the  largest  dog, 
but  the  total  metaboUsm  was  nearly  proportional  to 
the  surface  area  throughout.  Probably  the  most  satis- 
factory explanation  of  this  relation  is  that  offered  by  von 
Hosslin,  who  holds  ^  that  the  internal  work  and  the  conse- 
quent heat  production  in  the  body  are  substantially  pro- 
portional to  the  two-thirds  power  of  its  volume,  and  since 
the  external  surface  bears  the  same  ratio  to  the  volume,  a 
proportionality  necessarily  exists  between  heat  production 
and  surface. 

The  above  data  obtained  upon  dogs  show  these  relations 
strikingly  because  of  the  great  differences  in  size,  the  largest 
dog  ha\ing  practically  ten  times  the  weight  of  the  smallest. 
^  Quoted  from  Armsby's  Principles  of  Animal  Nuirition,  p.  368. 


CONDITIONS    AFFECTING   FOOD    REQUIREMENT       1 67 

In  the  human  species  where  the  variation  in  size  among 
adults  is  much  less,  the  discrepancies  in  heat  production 
per  unit  of  body  weight  are  much  smaller,  and  for  most  pur- 
poses it  is  sufficient  to  consider  the  resting  metabolism  of 
the  normal  adult  as  practically  proportional  to  the  body 
weight.  In  those  cases  in  which  the  surface  area  is  to  be 
considered,  it  is  usually  computed  from  the  weight  as 
follows :  — 

For  soKds  of  the  same  shape  the  surface  is  proportional 
to  the  two-thirds  power  of  the  volume ;  and  if  the  density  is 
also  constant,  the  surface  will  be  proportional  to  the  two- 
thirds  power  of  the  weight.  Hence,  if  S  represents  the  sur- 
face, W  the  weight,  and  C  a  constant  dependent  upon  the 
shape  and  density  of  the  solid,  we  have  S  =  C  ^W^  in 
which  (according  to  Meeh)  the  value  of  C  for  man  is  12.3. 

The  assumption  that  the  form  is  constant  in  the  same 
species  is  of  course  not  strictly,  correct.  A  tall,  thin  man 
exposes  more  surface  for  a  given  weight  than  does  a  short, 
stout  man.  Normal  men  may  vary  as  much  as  ten  per  cent 
from  the  average  in  the  relation  of  surface  to  weight.  The 
thin  man,  besides  having  a  greater  surface,  also  differs  from 
the  stout  man  in  that  a  larger  percentage  of  his  body  is 
actual  protoplasm.  Since  the  metabolism  of  the  body  de- 
pends upon  its  weight  of  protoplasm  (active  tissue)  rather 
than  its  total  weight,  we  have  here  an  important  reason 
for  believing  that  the  food  requirement  will  be  greater  in 
a  tall,  thin  man  than  in  a  shorter  and  fatter  man  of  the  same 


1 68  CHEMISTRY   OF   FOOD   AND   NUTRITION 

weight.  Von  Noorden  tested  this  question  by  observing  the 
metabolism  (for  one  day  without  food)  of  two  men  of  dif- 
ferent build  but  nearly  the  same  weight.  The  results 
were  as  follows:  — 

ist  man,  thin  and  muscular,  weight  71.1  kilograms;  2392 
calories  =  33.6  calories  per  kilogram. 

2d  man,  stout,  weight  73.6  kilogmms;  2136  calories  =  29.0  calo- 
ries per  kilogram. 

For  the  great  majority  of  persons,  however,  we  may  pro- 
ceed in  dietary  calculations  as  if  the  form  and  composition  of 
the  body  were  constant  without  introducing  serious  error. 

THE  INFLUENCE  OF  AGE   AND   SEX 

From  the  fact  that  in  animals  of  the  same  species,  but  of 
different  size,  the  heat  production  is  proportional  to  the  surface 
rather  than  to  the  weight,  it  would  follow  that  children  must 
have  a  greater  food  requirement  per  unit  of  weight  than 
adults.  By  observ^ation  it  is  found  that  the  heat  production 
(and  therefore  the  food  requirement)  is  not  only  greater  per 
unit  weight,  but  is  also  somewhat  greater  per  unit  of  surface, 
in  the  child  than  in  the  adult.  The  total  metabohsm  at  rest 
is  approximately  half  as  great  in  a  child  of  2  years  weighing 
25  poimds  as  in  an  adult  of  six  times  the  weight.  Here  the 
food  equivalent  per  unit  of  weight  is  three  times  as  great  for 
the  young  child  as  for  the  resting  man. 

The  following  data,  adapted  from  Tigerstedt,  illustrate  the 
relative  intensity  of  metabohsm  at  different  ages:  — 


CONDITIONS   AFFECTING   FOOD   REQUIREMENT       1 69 


Kilograms 

Metabolism  per  Day 

StJBJECT 

Total, 
calories 

Per  kilogram, 
calories 

Per  sq.  meter, 
calories 

Child,    2  weeks     .     . 
Child,  10  weeks     .     . 
Child,  10  years      .     . 
Man  at  rest       .     .     . 

3-2 

23.2 
70.0 

258 

420 

1462 

2240 

81 
84 
63 
32 

1000 
1200 
1499 
1071 

According  to  these  data  the  metabolism  per  unit  of  weight 
is  greatest  in  infancy  and  declines  steadily  with  increasing 
size ;  but  calculated  per  unit  of  surface,  it  is  distinctly  less  in 
infancy  than  in  children  of  10  years,  probably  because  the 
infant  sleeps  a  greater  proportion  of  the  time  and  the  tension 
(tonus)  of  its  muscles  is  not  yet  fully  developed. 

Camerer  made  a  large  number  of  observations  upon  the 
food  consumption  of  boys  of  different  ages  with  the  following 
average  results :  — 


Metabolism 

Weight, 
Kilograms 

Age,  Years 

Total, 

Per  kilogram. 

Per  sq.  meter, 

calories 

calories 

calories 

5-6 

18 

1386 

77 

1680 

7-10 

24 

1488 

62 

1440 

11-14 • 

34 

1598 

47 

1250 

15-16  

S3 

2120 

40 

1220 

17-18  

59 

2242 

38 

1200 

Magnus-Levy  and  Falck  observed  the  oxygen  consumption 
of  subjects  of  various  ages  while  lying  at  complete  rest  and 


lyo 


CHEMISTRY    OF    FOOD   AND   NUTRITION 


fasting.     The  following  are  typical  of  the  results  obtained 
with  boys :  — 


Age 


years 
2i  ... 

6     .     .     .  . 

lo  .     .     .  . 

14  ...  . 

16   ...  . 

22-43  •     •  • 


Weight 


kilograms 

18.4 
30.6 
36.1 

57-5 
66.7 


Oxygen  Consumption 


Total 


cc. 
112. 2 

139-9 
192.0 
188.1 
235-6 
227.9 


Per  kilogram 


cc. 
9.76 
7.61 
6.28 
5.21 
4.10 
3-41 


Per  kilogram 

compared  with 

adults 


per  cent 

285 
223 
184 
152 
120 
100 


Sonden  and  Tigerstedt  compared  the  metabolism  of  men 
and  boys  by  determining  the  carbon  dioxide  production  while 
sitting  up  and  at  only  a  short  time  after  a  meal.  Under  these 
conditions  (quite  different  from  those  obtaining  in  the  ex- 
periments of  Magnus-Levy  and  Falck)  they  obtained  results 
as  follows :  — 


Age 


Years 


9t  ■ 
io| 

11^ 

12^ 
14  . 
I4I 

i5i 

17   • 

19^ 

23 

25 

35 


Weight 


Kilograms 


28 
30 
32 
34 
45 
45 
51 
56 
60 

65 
68 

68 


Carbon  Dioxide  per  Hour 


Total 


33 
33 
34 

34 
45 
44 
42 

45 
43 

38 
38 
35 


Per  kilogram 


1. 21 
I. II 
1.06 
1. 00 
1. 00 
0.96 
0.81 
0.81 
0.72 
0.58 
0.57 
0.52 


Per  square 
meter 


29.9 
28.2 

27-5 
26.5 
27.6 
26.7 

23-5 
24.2 
21.8 

18.6 

i8.5 
16.9 


CONDITIONS    AFFECTING   FOOD   REQUIREMENT       171 

Here  the  intensity  of  metabolism  as  measured  by  the  car- 
bon dioxide  production  per  unit  of  surface  as  well  as  per  unit 
of  weight  decreases  steadily  with  increasing  age  from  the 
nine-year-old  child  to  the  adult.  In  these  cases  the  absolute 
production  of  carbon  dioxide  per  hour  (and  therefore  pre- 
sumably the  food  requirement  per  day)  was  greater  between 
the  ages  of  14  and  19  than  with  the  adult  of  considerably 
greater  weight.  This  may  be  explained  in  part  by  the  ra- 
pidity of  growth,  which  would  involve  increased  general  me- 
tabolism and  in  part  by  the  higher  muscular  tension  of 
boys  of  this  age  as  compared  with  most  men. 

The  results  of  Magnus-Levy  and  Falck  and  those  of  Sonden 
and  Tigerstedt  point  to  the  same  conclusions  except  that  the 
latter  found  a  more  intense  metabolism  in  boys  of  14  to  19 
years  than  the  former,  probably  on  account  of  the  fact  that 
their  observations  were  made  upon  boys  fully  fed  and  in  a 
higher  state  of  muscular  tone.  They  found  in  boys  a  carbon 
dioxide  production  about  40  per  cent  higher  than  in  girls  of  the 
same  weight,  which  also  was  attributed  to  the  greater  muscu- 
lar tension  and  restlessness  of  the  boys.  This  difference  is 
not  perceptible  in  the  data  obtained  by  Magnus-Levy  and 
Falck  with  children  fasting  at  complete  rest  nor  in  those  of 
Sonden  and  Tigerstedt  for  individuals  over  30  years  of  age. 
In  general,  it  appears  that  the  food  requirements  of  men  and 
women  of  equal  activity  are  in  proportion  to  their  body 
weights.  Women  on  the  average  weigh  about  0.8  as  much  as 
men,  and  it  is  commonly  assumed  that  if  equally  active  their 
food  requirements  will  stand  in  the  same  proportion. 


172  CHEMISTRY   OF   FOOD   AND  NUTRITION 

In  computing  the  results  of  dietary  studies  and  in  ap- 
portioning the  food  of  a  family  to  its  different  members  it 
has  become  customary  to  make  use  of  some  such  conven- 
tional factors  as  the  following :  Taking  the  food  requirement 
of  a  man  as  i,  that  of  women  and  of  boys  14-17  years  old  is 
taken  as  0.8 ;  of  girls,  14-17  years  old,  0.7 ;  children  of  10-13 
years,  0.6 ;  of  6-9  years,  0.5  ;  of  2-5  years,  0.4 ;  of  less  than 
2  years,  0.3.  These  factors  are  based  upon  the  food  require- 
ments of  men  engaged  in  moderately  active  work  (in  the 
sense  in  which  Voit  and  Atwater  have  used  the  expression), 
and  if  appUed  to  the  family  of  a  business  or  professional  man 
would  probably  result  in  too  low  an  estimate  of  the  food 
requirements  of  the  children.  The  food  requirement  of  a 
man  varies  so  greatly,  according  to  occupation,  that  it 
seems  hardly  logical  to  make  this  a  basis  for  estimating  the 
dietary  needs  of  a  family.  It  is  perhaps  more  satisfactory 
to  say  that  a  woman  requires  the  same  number  of  calories  per 
kilogram  (or  per  pound)  of  body  weight  as  does  a  man  of 
equal  activity;  and  that  children  of  normal  size,  develop- 
ment, and  activity  will  require  about  as  follows :  — 

Boys  of  14-17  years  2500-3000  calories. 
Girls  of  14-17  years  2200-2600  calories. 
Children  of  10-13  years  1800-2200  calories. 
Children  of  6-9  years  1400-2000  calories. 
Children  of  2-5  years  1 200-1 500  calories. 
Children  of    1-2    years    900-1200  calories. 

On  account  of  the  differences  in  size  among  children  of  the 
same  age,  it  is  desirable  to  give  the  food  requirement  in  terms 


CONDITIONS   APFECTING    FOOD   REQUIREMENT       1 73 

of  body  weight  as  well  as  of  the  average  individual.     Ap- 
proximate estimates  on  this  basis  are  as  follows:  — 

Under    i     year        100        calories  per  kilogram. 

1-2    years       100-90  calories  per  kilogram. 

2-5    years       90-80  calories  per  kilogram. 

6-9    years       80-70  calories  per  kilogram. 

10-13  years        70-60  calories  per  kilogram. 

14-17  years       60-45  calories  per  kilogram. 

The  fuel  value  of  children's  dietaries  should  always  be 
liberal  in  order  to  provide  amply  for  muscular  activity  and 
for  a  more  intense  general  metabolism  than  that  of  the  adult, 
as  well  as  because  throughout  the  period  of  growth  the  food 
must  supply  a  certain  amount  of  material  to  be  added  to  the 
body  in  the  form  of  new  tissue  in  addition  to  all  that  which 
is  oxidized  to  support  metaboHsm. 

With  the  elderly,  on  the  other  hand,  the  intensity  of  me- 
tabolism is  diminished,  and  the  body  not  only  needs  less  food, 
but  has  less  ability  to  deal  with  excess,  so  that  the  food  re- 
quirement gradually  declines  and  may  become  10, 20,  or  30  per 
cent  lower  than  in  middle  life.  Ekholm  found  in  the  average 
of  10  experiments  upon  persons  of  68  to  81  years  of  age  an 
average  metabolism  of  902  calories  per  square  meter  of  sur- 
face, whereas  the  usual  estimate  for  the  adult  is  107 1  calories. 

Von  Noorden  allows  for  the  normal  nutrition  of  young  to 
middle-aged  men  and  women  :  — 

At  complete  rest    ....  30-35  calories  per  kilogram  per  day. 

With  light  exercise     .     .     .  35-40  calories  per  kilogram  per  day. 

With  moderate  exercise  .     .  40-45  calories  per  kilogram  per  day. 

With  hard  muscular  labor  .  45-60  calories  per  kilogram  per  day. 


174 


CHEMISTRY    OF    FOOD   AND    NUTRITION 


He  states  that  for  children  these  figures  are  to  be  raised 
about  one  third  and  for  the  aged  they  are  to  be  lowered  about 
one  fourth. 

Remembering  that  children  should  normally  be  reckoned  as 
taking  at  least  moderate  exercise,  while  the  aged  will  probably 
be  either  at  rest  or  with  only  very  light  exercise,  it  will  be  seen 
that  as  regards  the  influence  of  age  Von  Noorden's  estimate 
and  that  above  given  are  in  substantial  agreement. 

In  the  following  table  are  given  the  estimated  heights, 
weights,  and  food  requirement  of  an  average  man  at  different 
ages,  the  figures  for  height  and  weight  being  based  upon  the 
data  given  by  Hill  for  males  of  the  Teutonic  races  {Recent 
Advances  in  Physiology  and  Biochemistry ^  p.  284) :  — 


Food  REQUiREME>rr 

Height 

Weight 

wiTHODT  Muscular 

Age, 

Labor 

Yeaks 

Meters 

Feet  and 
inches 

Kilos 

Pounds 

Total  per 

dav. 
calories 

Per  kilo- 
gram 
per  day, 
calories 

I 

0.70 

2:3 

10 

22 

1000 

ICX> 

5 

1. 00 

3:3 

17 

37 

1400 

82 

10 

1.28 

4:  2 

26 

57 

1800 

70 

IS 

50 

no 

2800 

56 

20 

1.71 

5:7^ 

65 

143 

3000 

46 

30 

1.72 

5:8- 

69 

152 

2750 

40 

40 

1. 71 

5:7^ 

70 

154 

2500 

36 

60 

65 

143 

2200 

34 

80 

60 

132 

1600 

27 

CONDITIONS    ATFECTING   FOOD    REQUIREMENT        1 75 

These  estimates  of  food  requirements  are  intended  to 
represent  approximate  averages  of  available  data  and  to  allow 
for  such  exercise  as  would  naturally  be  taken  at  the  age, 
exclusive  of  anything  which  would  ordinarily  be  considered 
physical  labor.  They  thus  illustrate  in  an  approximate  way 
the  rate  at  which  the  amount  of  food  required  for  healthy 
maintenance  per  unit  of  body  weight  decHnes  from  infancy 
to  old  age. 

REFERENCES 

Armsb Y.     Principles  of  Animal  Nutrition,  Chapters  6  and  1 1 . 
Atwater.     Neue  Versuche  ueber  Stoff-  und  Kraft-wechsel.     Ergebnisse 

der  Physiologie,  3  (1904). 
Atwater,   Benedict,   et   al.      Respiration    Calorimeter   Experiments, 

Bulls.  44,  63,  69,  109,  136,  175,  Office  of  Experiment  Stations,  U.  S. 

Dept.  Agriculture. 
Benedict.     The  Influence  of  Inanition  on  Metabolism.     Publication  No. 

77,  Carnegie  Institution,  Washington  (1907). 
Benedict  and  Carpenter.     The  Influence  of   Muscular  and  Mental 

Work  on  Metabolism  and  the  Efficiency  of  the  Human  Body,  as  a 

Machine.     Bull.    208,  Office  of   Experiment   Stations,  U.  S.  Dept. 

Agriculture  (1909). 
Hill.     Recent  Advances  in  Physiology  and  Biochemistry,  Chapters  8, 9, 

10,  15. 
Hutchison.    Food  and  Dietetics,  Chapters  2  and  3. 
Jaquet.     Der  respiratorische  Gaswechsel.     Ergebnisse  der   Physiologie, 

2,  457-574. 
LusK.     Elements  of  the  Science  of  Nutrition. 
Nagel.     Handbuch  der  Physiologie  des  Menschen,  pp.  375-480. 
Rubner.     Die  Gesetze  der  Energieverbrauches  bei  der  Ernahrung. 
Von  Noorden.    Metabolism  and  Practical  Medicine,  Vol.  I,  pp.  208-282. 


CHAPTER  VII 

PROTEIN   METABOLISM   AND   THE  PROTEIN 
REQUIREMENT 

Animal  cells  under  all  conditions  of  life  are  constantly 
breaking  down  proteins  into  simpler  substances  which  the 
body  eUminates.  This  breaking  down  or  ''kataboUsm"  of 
protein  does  not  stop  either  in  fasting  or  under  the  most 
liberal  feeding  wath  fats  and  carboyhdrates,  so  that  there  is 
always  a  need  for  protein  whatever  the  supply  of  other  food. 

The  protein  metaboUsm  differs  wadely  from  the  total  me- 
tabolism in  the  conditions  which  determine  its  amoimt,  for 
the  protein  metabolism  is  governed  mainly  by  the  food,  and 
to  only  a  sUght  extent  by  the  muscular  exercise ;  whereas  the 
total  metabolism  is  governed  mainly  by  the  amount  of  ex- 
ercise, and  to  only  a  slight  extent  by  the  food.  By  giving 
food  rich  in  fats  and  carbohydrates  but  poor  in  protein,  the 
protein  metabolism  of  a  healthy  man  can  easily  be  brought  to 
50  grams  per  day,  and  then,  by  changing  to  a  diet  rich  in  pro- 
tein, it  may  be  increased  to  150  or  even  200  grams  per  day ; 
i.e.  the  rate  of  protein  metabolism  can  be  increased  200  to 
300  per  cent  in  a  few  days  by  a  change  in  diet  alone,  all  other 
conditions  remaining  the  same. 

Since  the  diet  has  such  a  great  influence  upon  the  amount 
of  protein  metabolized,  it  might  be  expected  that  the  essential 

176 


PROTEIN   METABOLISM   AND   PROTEIN   REQUIREMENT       1 77 


protein  metabolism  could  be  observed  best  in  fasting.  But 
in  fasting,  the  energy  metabolism  of  the  body  is  only  a  Httle 
lower  than  with  food;  the  amount  of  combustion  continues 
nearly  the  same  although  only  body  material  is  available;  and 
since  the  body  must  consume  so  much  of  its  own  substance  as 
fuel  in  fasting,  there  is  always  a  chance  that  the  protein  may 
be  burned  simply  as  fuel  and  thus  that  the  protein  metaboHsm 
in  fasting  may  be  greater  than  that  which  represents  the 
needs  of  the  body  when  properly  fed,  while  on  the  other  hand 
it  may  be  abnormally  low  through  the  effort  of  the  body  to 
adjust  itself  to  the  abnormal  condition. 

The  amount  of  protein  broken  down  in  fasting  is  much 
influenced  by  the  previous  habit  as  regards  protein  consump- 
tion, and  by  the  metabohsm  of  stored  glycogen  and  stored  fat. 

The  direct  effect  of  the  habit  of  protein  metabolism  estab- 
lished by  the  feeding  of  the  days  preceding  the  fast  is  shown 
in  the  following  data  obtained  by  Voit  in  experiments  upon  a 
dog  weighing  35  kilograms:  — 

Influence  of  Previous  Diet  on  Nitrogen  Elimination  in  Fasting 

(Voit) 


Grams  of  Urea  per 

Day 

Food  of  Preceding  Days 

Meat  2500  grams 

Meat  1500  grams 

Bread 

Last  day  with  food     .     .     . 

180.8 

II0.8 

24.7 

First  day  of  fasting    .     .     . 

60.1 

29.7 

19.6 

Second  day  of  fasting      .     . 

24.9 

18.2 

15.6 

Third  day  of  fasting  .     .     . 

19.I 

17-5 

14.9 

Fourth  day  of  fasting      .     . 

17-3 

14.9 

13.2 

Fifth  day  of  fasting    .     i     . 

12.3 

14.2 

12.7 

Sixth  day  of  fasting    .     .     . 

13-3 

13.0 

13-0 

178 


CHEMISTRY    OF    FOOD    AND    NUTRITION 


The  influence  of  the  metabolism  of  the  pre\dously  stored 
glycogen  upon  the  amount  of  protein  metabolized  in  fasting 
is  well  illustrated  by  the  following  three  experiments  with  one 
individual :  ^  — 


First  Day 

OF  Fasting 

Second  Day 

OF  Fasting 

Glycogen 

Nitrogen 

Glycogen 

Nitrogen 

metabolized 

eliminated 

metabolized 

eliminated 

grams 

grams 

grams 

grams 

I 

181.6 

5-84 

29.7 

11.04 

n 

135-3 

10.29 

18.I 

11.97 

ni 

64.9 

12.24 

23.1 

12.45 

It  will  be  seen  that  the  nitrogen  output  was  less  when  there 
was  available  for  metabolism  a  considerable  supply  of  pre- 
viously stored  glycogen.  Since  most  of  the  stored  glycogen 
is  used  up  on  the  first  day  of  fasting,  its  influence  upon  the 
protein  metabolism  is  short-lived  as  compared  with  that  of 
the  stored  fat. 

The  influence  of  the  available  supply  of  body  fat  upon  the 
protein  metabolism  of  fasting  is  shown  by  the  following  ob- 
servations of  Falck  on  the  protein  metaboUsm  of  two  fast- 
ing dogs  —  the  one  lean,  the  other  fat. 

A  rise  in  protein  metabolism  of  the  lean  dog  after  the  8th 
day  showed  that  from  this  time  he  used  protein  largely  as 
fuel — so  largely  that  the  results  were  fatal  in  25  days  of  fast- 

^  Benedict,  Influence  of  Inanition  on  Metabolism.  Carnegie  Institu- 
tion of  Washington,  1907. 


PROTEIN    METABOLISM   AND   PROTEIN    REQUIREMENT       1 79 


Falck's  Lean  Dog 

Falck's  Fat  Dog 

Katabolized  on  days 

Grams  protein 
per  day 

Katabolized  on  days 

Grams  protein 
per  day 

1-4 

26.1 

1-6 

29.9 

5-8 

24.6 

7-12 

26.7 

9-T2 

33-9 

13-18 

26.1 

13-16 

38.0 

19-24 

22.3 

17-20 

31-9 

25-29 

20.0 

21-24 

3-9 

30-34 

16.8 

On  the  25  th  day  the  dog  died. 

35-38 

15-7 

40-44 

13.0 

45-50 

13.6 

55-60 

12.2 

Dog  still  healthy  after  60  days. 

ing.  The  fat  dog,  having  plenty  of  other  fuel  in  the  form 
of  fat,  used  protein  to  a  much  smaller  extent,  so  that  he  was 
able  gradually  to  accommodate  himself  to  a  lower  level  of 
protein  metabolism  and  to  endure  a  fast  of  60  days'  duration. 
The  professional  faster,  Succi,  starting  with  a  good  store 
of  body  fat,  fasted  30  days  with  the  following  results :  — 


Five  days  on  ordinary  food 

I-  5th  days  fasting  ,  . 

6-1  oth  days  fasting  .  . 

ii-i5th  days  fasting  .  . 

1 6- 20th  days  fasting  .  , 

2i-25th  days  fasting  .  . 

26-3oth  days  fasting  .  . 


101.4  grams  protein  per  day. 
80.4  grams  protein  per  day. 

53.1  grams  protein  per  day. 

36.2  grams  protein  per  day. 
33,1  grams  protein  per  day. 

29.3  grams  protein  per  day. 
33.3  grams  protein  per  day. 


Since  Succi's  health  remained  good  throughout  his  fast, 
it  might  be  thought  that  the  necessary  waste  of  protein  from 


l8o  CHEMISTRY    OF   FOOD   AND   NUTRITION 

his  body  was  not  greater  than  the  smallest  figure  found  for 
any  period  —  in  this  case  about  30  grams  per  day.  On 
the  other  hand,  it  may  well  be  supposed  that,  since  the 
body  increases  its  protein  metabolism  to  an  abnormally 
high  rate  imder  influence  of  excessive  protein  feeding,  so 
under  the  influence  of  fasting  the  body  may  be  able  to  ad- 
just itself  to  an  abnormally  low  rate  of  protein  metabolism; 
and  the  fact  that  the  protein  metabolism  continues  to  di- 
minish for  such  a  long  time  in  fasting  gives  weight  to  the 
supposition  that  the  body  is  here  gradually  adapting  itself 
to  an  abnormal  condition.  One  might  assume  that  in  the 
first  or  second  five-day  period  of  Succi's  fast  the  effect  of 
previous  feeding  might  have  worn  off  suflSciently,  and  the 
conditions  not  yet  have  become  abnormal  as  the  result  of 
the  fasting,  in  which  case  the  expenditure  of  protein  during 
one  of  these  periods  would  represent  his  normal  require- 
ment. Any  such  assumption  must,  however,  be  more  or  less 
arbitrary. 

Of  interest  in  this  connection  are  the  data  of  nitrogen  ex- 
cretion obtained  by  Benedict  in  his  recent  study  of  the  me- 
tabolism of  several  subjects  during  fasting  periods  of  2  to  7 
days'  duration.  There  were  great  irregularities  in  the  results 
for  the  first  day,  probably  due  in  large  part  to  the  previous 
conditions  of  feeding.  The  average  of  all  observations  for 
the  second  day  of  fasting  shows  12.8  grams  of  nitrogen  cor- 
responding to  80  grams  of  protein,  and  for  all  observations 
of  subsequent  days  11.8  grams  of  nitrogen  or  74  grams  of 


PROTEIN   METABOLISM   AND   PROTEIN   REQUIREMENT       l8l 

protein,  whereas  Sued  metabolized  during  the  first  to  fifth 
days  of  his  fast  80  grams  and  during  the  sixth  to  tenth  days 
53  grams  of  protein  per  day.  Such  data  of  protein  metab- 
ohsm  during  fasting  (of  which  many  more  might  be  cited) 
undoubtedly  throw  light  upon  the  requirement,  but,  as 
suggested  above,  they  may  be  interpreted  in  such  different 
ways  as  to  make  it  doubtful  how  far  they  should  be  accepted 
as  indicating  the  amount  of  protein  which  the  food  should 
normally  furnish. 

An  idea  of  the  normal  dietary  need  is  best  obtained  by 
determining  experimentally  how  much  protein  must  be  con- 
tained in  the  daily  food  in  order  to  keep  the  body  in  pro- 
tein (or  nitrogen)  equilibrium. 

The  estimation  of  the  nitrogen  balance  has  already  been 
referred  to  as  one  factor  in  the  determination  of  the  total  food 
requirement  by  means  of  metabolism  experiments;  and  it 
has  been  shown  that  the  balance  may  be  found  either  by 
comparing  the  total  intake  with  the  total  output,  or  by  com- 
paring the  amount  absorbed  with  the  amount  katabolized 
and  eliminated  through  the  kidneys.^  A  plus  balance  in- 
dicates a  storage  of  nitrogen  and  therefore  of  protein  in  the 
body;  a  minus  balance  indicates  a  loss  of  body  protein. 
When  the  balance  is  o,  or  so  near  o  as  to  be  within  the 

1  Theoretically  the  elimination  through  the  skin  should  also  be  deter- 
mined and  included  in  the  calculation ;  practically  this  is  usually  neg- 
lected unless  on  account  of  warm  weather  or  vigorous  exercise  the  subject 
has  perspired  profusely.  For  data  on  nitrogen  in  perspiration  see  Bene- 
dict, Journal  of  Biological  Chemistry,  i,  263  (1906). 


l82 


CHEMISTRY    OF   FOOD    AND    NUTRITION 


limits  of  experimental  error,  the  body  is  said  to  be  in 
nitrogen  {or  protein)  equilibrimn. 

The  healthy  full-grown  body  tends  to  establish  nitrogen 
equilibrium  by  adjusting  its  rate  of  protein  katabolism  to  its 
food  supply  within  wide  limits.  The  time  required  by  the 
body  for  this  adjustment  depends  mainly  upon  the  extent 
to  which  the  diet  is  changed. 

The  following  observations  by  Von  Noorden  illustrate 
the  establishment  of  equilibrium  after  only  moderate  changes 
in  the  diet. 

A  young  woman  weighing  58  kilograms  (128  pounds) 
at  rest  in  bed  was  given  food  furnishing  protein,  106  grams ; 
fat,  71.6  grams;  carbohydrate,  200  grams;  fuel  value,  i860 
calories  per  day. 

Total  nitrogen  in  food 16.96  grams 

Lost  in  digestion .94  grams 

Absorbed       16.02  grams 


Katabolized  and  Eliminated  through  Kidneys 

Balance 

ist  day 

2d  day 

3d  day 

4th  day 

5th  day 

grams 
18.2 
17.0 
15.8 
16.0 
15.7 

grams 

-  2.18 

-  0.98 
+  0.22 
+  0.02 
+  0.32 

Here  there  was  practical  equilibrium  after  the  second  day. 
The  small  amount  of  nitrogen  represented  as  stored  on  the 
third,  fourth,  and  fifth  days  was  very  likely  lost  through  the 


PROTEIN    METABOLISM   AND   PROTEIN   REQUIREMENT       1 83 

skin.  This  was  a  case  of  adjustment  to  a  lowered  protein 
intake,  for  the  food  previously  taken,  although  not  accu- 
rately observed,  was  known  to  have  been  rich  in  protein. 

Another  experiment  was  made  by  Von  Noorden  with  the 
same  patient  to  show  the  time  required  to  reach  equilibrium 
after  increasing  the  intake  of  protein.  In  this  case  the  food 
furnished  2030  calories  per  day  and  the  nitrogen  balance 
was  as  follows :  — 


Day 

Nitrogen 
IN  Food 

Lost  in 
Digestion 

Absorbed 

Katabolized 

Balance 

grams 

grams 

grams 

grams 

grams 

I 

14.40 

0.70 

13.70 

13.60 

+  O.IO 

2 

14.40 

0.70 

13.70 

13.80 

—  O.IO 

3 

14.40 

0.70 

13.70 

13.60 

+  O.IO 

4 

20.96 

0.82 

20.14 

16.80 

+  3.34 

5 

20.96 

0.82 

20.14 

18.20 

+  1.94 

6 

20.96 

0.82 

20.14 

19.50 

+  0.64 

7 

20.96 

0.82 

20.14 

20.00 

+  0.14 

Here  where  the  amount  of  protein  fed  was  increased  from 
90  to  130  grams  without  change  in  the  total  fuel  value  of 
the  diet,  the  body  reached  equilibrium  on  the  fourth  day. 

It  is  apparent  therefore  — 

(i)  That  the  body  tends  to  adjust  its  protein  katabolism 
to  its  protein  supply. 

(2)  That  when  the  body  is  accustomed  to  a  certain 
rate  of  protein  katabolism,  it  requires  an  appreciable  length 
of  time  to  adjust  itself  to  a  higher  or  lower  rate. 


184  CHEMISTRY    OF   FOOD    AND   NUTRITION 

Hence  the  rate  of  protein  katabolism  on  any  given  day 
will  depend  in  part  upon  the  protein  intake  for  that  day  and 
in  part  upon  the  rate  of  katabolism  to  which  the  body  has 
been  accustomed  upon  the  preceding  days.  When  the  pro- 
tein supply  is  constant  for  a  few  days,  the  effect  of  previous 
habit  disappears  and  equilibrium  is  established  as  in  the 
above  cases.  When  the  protein  supply  varies  from  day  to 
day,  the  kataboUsm  for  each  day  is  influenced  by  both  the 
factors,  with  the  net  result  that  the  elimination  equals  the 
intake  when  averaged  for  a  sufficiently  long  period,  although 
the  data  for  any  particular  day  might  show  a  distinct  gain  or 
loss. 

A  transitory  loss  of  nitrogen  from  the  body  is  apt  to  be  due 
simply  to  the  taking  of  less  than  the  usual  amount  of  protein 
food,  but  a  persistent  loss  indicates  that  the  diet  is  insuffi- 
cient, either  in  total  food  (calories)  or  in  protein,  to  enable 
the  usual  adjustment  to  take  place. 

A  transitory  storage  of  nitrogen  in  the  body  may  occur  as 
the  result  of  an  increase  either  of  the  protein  or  of  the  total 
fuel  value  of  the  food,  but  a  persistent  storage  occurs,  as 
Von  Noorden  has  pointed  out,  only  under  the  following  con- 
ditions:— 

(i)  In  the  growing  body  (or  in  pregnancy)  where  new 
tissue  is  being  constructed. 

(2)  In  cases  where  increased  muscular  exercise  calls  for 
enlargement  of  the  muscles. 

(3)  In  cases  where,  owing  to  pre\dous  insufficient  feeding 


PROTEIN   METABOLISM   AND   PROTEIN   REQUIREMENT      1 85 

or  to  wasting  disease,  the  protein  content  of  the  body  has 
been  more  or  less  diminished  and  consequently  any  surplus 
available  is  utilized  to  make  good  the  loss. 

It  has  already  been  shown  that  the  fuel  value  of  the  food 
has  a  great  influence  upon  the  protein  metabolism  by  deter- 
mining whether  or  not  the  body  must  draw  upon  its  own 
tissues  for  fuel.  That  the  rate  of  protein  katabolism  can  be 
decreased  by  the  feeding  of  carbohydrates  or  fats  was  known 
before  the  development  of  our  present  conceptions  of  the  en- 
ergy metabolism,  and  this  property  of  the  carbohydrates 
and  fats  was  designated  their  "protein  sparing"  or  "protein 
protecting"  power.  Thus  the  loss  of  protein  which  occurs 
in  an  insufficient  diet  may  be  diminished  or  even  stopped  by 
adding  carbohydrates  or  fat  to  the  food ;  and  if  carbohydrate 
or  fat  be  added  to  the  diet  of  a  man  in  nitrogen  equilibrium, 
there  results  a  temporary  decrease  in  nitrogen  output  with  a 
corresponding  storage  of  protein  in  the  body.  For  an  account 
of  the  earlier  experiments  on  this  subject,  especially  those  of 
Voit  and  Rubner  upon  dogs,  the  reader  is  referred  to  Lusk's 
Elements  of  the  Science  of  Nutrition.  Only  some  of  the  more 
important  of  the  experiments  upon  men  wdll  be  described  here. 

Lusk,^  experimenting  upon  himself,  showed  the  suscepti- 
bility of  the  protein  metabolism  to  the  sudden  withdrawal  of 
carbohydrate  food.  In  one  experiment  a  liberal  mixed  diet 
containing  20.55  grams  of  nitrogen  was  taken  until  the  body 
was  nearly  in  nitrogen  equilibrium,  and  then,  without  any 
^  Zeitschrift  fur  Biologie,  27,  459  (1890). 


1 86  CHEMISTRY   OF   FOOD   AND   NUTRITION 

Other  change,  350  grams  of  carbohydrate  were  withdrawn  from 
the  daily  food.  On  the  first  day  the  body  protein  was  largely 
protected  by  the  carbohydrate  previously  stored  in  the 
body  in  the  form  of  glycogen,  but  on  the  second  day  the 
nitrogen  metabolism  had  risen  from  19.84  to  27.00  grams 
per  day.  In  another  experiment,  upon  a  diet  containing  less 
protein,  withdrawal  of  carbohydrate  increased  the  nitrogen 
excretion  from  11.44  to  17.18  grams  per  day. 

From  the  data  of  these  and  three  similar  experiments  tabu- 
lated by  Von  Noorden  it  appears  that  the  extra  protein 
metabolized  as  the  result  of  withdrawal  of  carbohydrate 
furnished  7  to  17  per  Cent  of  the  energy  of  the  carbohydrate 
withdrawn,  so  that  if  there  was  no  change  in  the  energy  me- 
tabolism, the  body  must  have  obtained  the  other  83  to  93  per 
cent  of  the  deficit  from  combustion  of  its  own  fat.  In  these 
cases,  as  in  the  fasting  experiments,  the  loss  of  body  pcotein 
was  less  in  those  subjects  having  a  good  store  of  body  fat  than 
in  those  which  were  thin. 

Kayser  ^  compared  the  eflSciency  of  carbohydrates  and  fats 
as  sparers  of  protein  by  observing  the  effect  upon  the  nitrogen 
balance  of  replacing  the  carbohydrates  of  the  food  by  such  an 
amount  of  fat  as  would  furnish  the  same  number  of  calories, 
and  then  after  three  days  resuming  the  original  diet.  The 
observer,  who  served  as  his  own  subject,  was  23  years  old, 

^  This  experiment  and  that  of  Tallquist  which  follows  are  given  some- 
what fully,  as  they  illustrate  well  the  methods  and  results  of  investigations 
based  mainly  upon  the  question  of  nitrogen  equilibrium. 


PROTEIN   METABOLISM   AND   PROTEIN   REQUIREMENT      1 87 

of  good  physique,  with  a  small  store  of  body  fat,  and  weighed 
67  kilograms.  In  the  first  and  third  periods  he  ate  meat, 
rice,  butter,  cakes,  sugar,  oil,  vinegar,  and  salad.  In  the 
second  period  the  diet  was  changed  so  as  to  consist  of  meat, 
eggs,  oil,  vinegar,  and  salad,  so  that  practically  all  the  carbo- 
hydrate was  withdrawn  and  replaced  by  fat.  The  two  diets 
had  practically  the  same  fuel  value  and  protein  contents. 
The  results  of  this  experiment  are  shown  in  the  following 
table :  — 

Kayser's  Table  Showing  Nitrogen  Balance  when  Feeding 
IsoDYNAjviic  Quantities  of  Carbohydrate  and  Fat 


Intake 

Output 

Total 

Nitrogen 

Mttp  nmrv 

Day 

Total 
Nitrogen 

Fat 

Carbo- 
hydrates 

Fuel 
value 

Balance 

grams 

grams 

grams 

calories 

grams 

grams 

I 

21.15 

71. 1 

338.2 

2590 

18.66 

+  2.46 

2 

21.15 

71.8 

338.2 

2596 

20.04 

-f-I.II 

3 

21.15 

71.8 

338.2 

2596 

20.59 

+  0.56 

4 

21.31 

71.8 

338.2 

2600 

21.31 

±  0.00 

5 

21.51 

221. 1 

0 

2607 

23.28 

-  1-77 

6 

21.55 

217.0 

0 

2570 

24.03 

-  2.48 

7 

21.55 

215.5 

0 

2556 

26.53 

-4.98 

8 

21.10 

70.4 

338.2 

2581 

21.65 

-0.55 

9 

21.10 

70.4 

338.2 

2581 

19.20 

+  1.89 

10 

21.10 

70.4 

338.2 

2581 

19.65 

+  1.45 

It  is  evident  from  the  nitrogen  balance  of  the  first  period 
that  the  amount  of  protein  in  the  food  was  here  greater  than 
necessary,  but  that  equilibrium  was  fully  established  in  four 


1 88  CHEMISTRY    OF   FOOD   AND    NUTRITION 

days.  On  substituting  fat  for  carbohydrate  there  is  a  marked 
increase  of  protein  katabolism  with  corresponding  loss  of  nitro- 
gen from  the  body,  and  what  is  especially  noteworthy,  there  is 
no  evidence  of  any  tendency  to  regain  equilibrium  during  this 
period,  but  on  the  contrary  the  loss  of  nitrogen  became  greater 
each  day  the  fat  diet  was  continued ;  whereas,  upon  returning 
to  the  mixed  diet,  not  only  w^as  the  loss  of  protein  stopped, 
but  the  body  almost  at  once  began  replacing  the  protein  it 
had  lost,  although  the  nitrogen  and  calories  of  the  food  were 
practically  unchanged. 

Tallquist  ^  compared  the  protein-protecting  powers  of  isody- 
namic  amounts  (amounts  ha\'ing  equal  energy  value)  of  carbo- 
hydrates and  fats  when  only  a  part  of  either  was  replaced  by 
the  other.  The  subject  was  Tallquist  himself,  a  man  28  years 
old,  in  good  health,  and  weighing  about  80  kilograms.  The 
experiment  was  performed  in  Rubner's  laboratory,  and  the 
diet  contained  such  an  amount  of  total  food  as  was  estimated 
by  Rubner  to  be  just  about  sufficient  to  supply  the  energy 
requirements  of  the  body,  viz.  36  calories  per  kilogram  per 
day.  The  experiment  covered  8  days  divided  into  two  equal 
periods.  In  the  first  four-day  period  the  diet  w^as  rich  in 
carbohydrates,  in  the  second  period  it  w^as  rich  in  fats.  An 
excellent  feature  of  this  experiment  is  that  there  was  no  change 
in  the  nature  of  the  protein  fed.  All  foods  furnishing  any  sig- 
nificant amount  of  nitrogen  were  the  same  in  the  two  periods 
of  the  experiment. 

*  Archivfiir  Hygiene,  41,  177. 


A. 


PROTEIN   METABOLISM   AND    PROTEIN   REQUIREMENT       1 89 

The  food  of  the  first  period  consisted  of  meat,  milk,  butter, 
bread,  sugar,  coffee,  beer.  That  of  the  second  period  con- 
tained the  same  amounts  of  meat,  milk,  bread,  coffee,  and  beer, 
but  less  sugar,  more  butter,  and  some  bacon.  The  same 
amoimt  of  salt  was  taken  in  each  case.  The  principal  data  of 
the  experiment  may  be  summarized  as  follows :  — 


Intake 

Output 

Day 

Nitrogen 

Total  ni- 
trogen 

Fat 

Carbohy- 
drate 

Alcohol 

Fuel 
value 

Nitrogen 

Balance 

grams 

grams 

grams 

grams 

calories 

grams 

grams 

I 

16.27 

44.0 

466 

18.5 

2867 

17.11 

-  0.84 

2 

16.27 

44.0 

466 

18.5 

2867 

14.40 

+  1.86 

3 

16.27 

44.0 

466 

18.S 

2867 

14.65 

+  1.62 

4 

16.27 

44.0 

466 

18.5 

2867 

15-58 

+  0.69 

5 

16.08 

140.0 

250 

19.0 

2873 

17.66 

-1.58 

6 

16.08 

140.0 

250 

19.0 

2873 

17.32 

-  1.24 

7 

16.08 

140.0 

250 

19.0 

2873 

15.94 

+  0.14 

8 

16.08 

140.0 

250 

19.0 

2873 

16.22 

-0.14 

Here  only  a  part  of  the  carbohydrate,  about  half  of  that 
present,  and  an  amount  representing  about  one  third  of  the 
total  fuel  value  of  the  diet,  was  replaced  by  fat.  The  change 
evidently  had  an  unfavorable  influence  upon  the  nitrogen 
balance,  but  the  loss  of  body  protein  was  relatively  small 
and  continued  only  2  days. 

Landergren  ^  also  found  that  it  is  only  when  the  carbohy- 

^  Skandanavisches  Archiv  fiir  Physiologie,  14,  112  (1903);  Abstract 
Experiment  Station  Record,  14,  1099. 


I  go  CHEMISTRY    OF   FOOD    AND    NUTRITION 

drate  of  the  diet  is  entirely  replaced  by  fat  that  the  com- 
parison is  so  strikingly  against  the  fat  as  it  seemed  to  be  in 
Kayser's  experiment.  In  Landergren's  experiments  the 
condition  studied  was  not  one  of  approximate  equilibrium, 
but  rather  of  nitrogen  hunger.  He  fed  men  diets  of  adequate 
fuel  value  but  containing  only  about  one  gram  of  nitrogen 
daily,  and  found  that  by  four  days  of  such  feeding  the 
urinary  nitrogen  may  be  reduced  to  about  4  grams  per 
day.  In  one  experiment  in  which  the  daily  food  contained 
750  grams  of  carbohydrates  the  urine  of  the  fourth  day 
showed  3.76  grams  of  nitrogen.  The  carbohydrate  was  then 
entirely  replaced  by  fat,  with  the  result  that  the  following 
days'  urines  contained  respectively  4.28,  8.86,  and  9.64 
grams  of  nitrogen.  Evidently  in  the  case  of  a  man  ac- 
customed to  feeding  largely  upon  carbohydrates  the  com- 
plete replacement  of  carbohydrate  by  fat  leads  to  a  loss  (or 
an  increased  loss)  of  body  protein.  But  by  subsequent 
experiments  of  the  same  series  it  was  found  that  a  diet 
containing  nearly  half  its  calories,  in  carbohydrate,  and 
nearly  half  in  fat,  had  apparently  the  same  protein-sparing 
power  as  one  made  up  almost  exclusively  of  carbohydrates. 
The  explanation  offered  by  Landergren  is  that  when  the 
diet  supplies  no  carbohydrate,  the  glycogen  of  the  body  soon 
l^ecomes  exhausted  and  the  carbohydrate  needed  to  keep 
up  the  constant  glucose  content  of  the  blood  is  obtained  largely 
by  the  breaking  down  of  proteins,  which  presumably  yield 
carbohydrate  in  metabolism  more  readily  than  do  the  fats. 


PROTEIN   METABOLISM   AND    PROTEIN    REQUIREMENT      IQI 

Atwater  ^  compared  the  protein-sparing  power  of  carbohy- 
drate and  fat  in  experiments  in  which  the  subject,  an  athletic 
young  man  of  76  kilos,  performed  a  considerable  amount  of 
work.  The  experiments  were  carried  out  in  the  respiration 
calorimeter  and  covered  in  all  15  experimental  days  upon  a 
diet  rich  in  carbohydrates,  arranged  in  four  periods  which 
were  alternated  with  four  equal  periods  in  which  the  diet  was 
rich  in  fats.  The  change  from  carbohydrate  to  fat  and  vice 
versa  involved  about  2000  calories  or  nearly  half  the  fuel  value 
of  the  diet.  The  average  results  per  day  for  the  entire  series 
of  experiments  were  as  follows :  — 


On  Diet  Rich  in 
Carbohydrates 

On  Diet  Rich  in 
Fat 

Available  calories  in  food  .... 

Heat  equivalent  of  work  performed, 

calories 

4532 

558 
17-5 

2-5 

16.6 
-1.6 

4524 

554 
17.1 

1-7 

18.1 

-2.7 

Nitrogen  in  food,  grams    .... 
Nitrogen  in  feces,  grams    .... 
Nitrogen  in  urine,  grams   .... 
Nitrogen  balance,  grams    .... 

Here  again  there  is  a  difference  in  favor  of  the  carbohydrate, 
but  one  which  is  so  small  as  to  be  of  almost  no  practical 
significance. 

It  appears  that  the  carbohydrate  of  the  food  cannot  be 
entirely  replaced  by  an  equal  number  of  calories  in  the  form 


*  Ergebnisse  der  Physiologie,  3,  Part  I,  p.  497. 


192  CHEMISTRY    OF    FOOD    AND    NUTRITION 

of  fat  without  an  unfavorable  effect  upon  the  nitrogen  balance, 
but  that  when  the  replacement  is  such  as  to  affect  not  over 
one  half  of  the  total  calories,  the  difference  in  protein-sparing 
power  is  but  slight,  and  that  ordinarily  on  a  normal  mixed 
diet  the  same  number  of  calories  has  practically  the  same 
protein- sparing  effect  whether  taken  mainly  as  carbohydrate 
or  mainly  as  fat.  Hence,  in  considering  the  influence  of  the 
fuel  value  of  the  food  upon  the  amount  of  protein  katabolized, 
it  is  usually  sufficient  to  know  the  total  calories  without 
regard  to  the  extent  to  which  they  are  derived  from  carbohy- 
drates or  from  fats. 

Different  observers  investigating  the  protein  requirement 
by  means  of  experiments  upon  nitrogen  equilibrium  have 
reached  very  different  conclusions,  largely  because  they  have 
used  diets  of  very  different  fuel  values.  Thus,  Neimiann  with 
a  diet  furnishing  2780  calories  required  about  80  grams  of 
protein,  while  Klemperer,  whose  food  had  a  fuel  value  of  5600 
calories,  was  able  to  maintain  equilibrium  on  about  25  grams 
of  protein  per  day.  Ordinarily  there  could  be  no  advantage  in 
thus  reducing  the  protein  katabolism  to  an  abnormally  low 
level  by  the  use  of  an  enormous  excess  of  fats  and  carbo- 
hydrates. 

For  practical  purposes,  therefore,  we  may  eliminate  the 
question  of  how  far  the  protein  metabolism  can  be  restricted 
by  the  use  of  excessive  amounts  of  other  food  and  reduce  the 
problem  to  this :  WTien  the  total  food  is  properly  adjusted  to 
the  muscular  activity  of  the  subject  so  that  there  is  ample  but 


PROTEIN    METABOLISM   AND   PROTEIN    REQUIREMENT       1 93 

not  excessive  fuel  to  meet  all  the  energy  requirements,  how 
much  protein  must  the  daily  food  contain  in  order  to  keep  the 
body  in  nitrogen  equilibrium  ? 

A  number  of  investigations  bear  more  or  less  directly  upon 
this  problem.  Among  the  earliest  and  most  striking  of  these 
is  that  of  Siven,  who,  experimenting  upon  himself  (body 
weight  60  kilograms),  found  that  with  a  diet  furnishing  41.4 
calories  per  kilogram  per  day  he  could  maintain  equilibrium 
upon  39  grams  of  protein,  while  with  the  same  fuel  value  and 
28  grams  of  protein  or  with  43  calories  per  kilogram  and  only 
25  grams  of  protein  per  day,  the  loss  of  body  nitrogen,  though 
persistent,  was  small  —  only  0.3  to  0.4  gram  of  nitrogen, 
corresponding  to  a  loss  of  2  or  2.5  grams  of  protein  per  day. 
Undoubtedly  Siven's  protein  requirement  was  less  than  that 
of  most  men. 

The  most  extended  investigation  on  the  protein  require- 
ments of  men  receiving  food  of  normal  fuel  value  is  that  of 
Chittenden.^ 

The  general  plan  followed  by  Chittenden  was  to  have  each 
man  reduce  his  protein  food  gradually  without  any  great 
change  in  his  other  habits.  This  gradual  reduction  of  the 
protein  intake  was  continued  sometimes  for  several  weeks, 
sometimes  for  several  months,  before  any  comparison  of  intake 
and  output  was  attempted.  During  this  long  preliminary 
period  upon  a  restricted  diet  there  was  in  almost  every  case 

^  See  Chittenden's  Physiological  Economy  in  Nutrition  and  Nutrition 
of  Man.  > 


194  CHEMISTRY    OF   FOOD    AND    NUTRITION 

a  loss  of  weight,  and  from  many  previous  observations  ^ 
under  similar  conditions  we  may  safely  assume  that  there 
was  a  considerable  loss  of  body  protein.  But  after  a  suffi- 
ciently long  period  of  loss,  there  was  usually  a  tendency  for 
the  body  weight  and  the  rate  of  protein  metaboUsm  (measured 
by  the  amount  of  nitrogen  eliminated  through  the  kidneys) 
to  become  fairly  constant,  indicating  that  the  body  had  ad- 
justed itself  to  the  new  conditions.  When  this  point  had 
been  reached,  a  nitrogen  balance  experiment  was  made,  and 
the  balance  of  intake  and  output  determined  by  weighing 
and  analyzing  for  nitrogen  all  food  consumed  and  all  ni- 
trogenous material  given  off  from  the  body  except  that  in 
the  perspiration.  At  the  same  time  the  fuel  value  was  cal- 
culated by  means  of  figures  taken  from  standard  tables. 
Assuming  that  these  calculated  fuel  values  are  approximately 
correct,  it  appears  that  the  total  food  consumed  by  Chit- 
tenden's subjects  was  in  general  about  equal  to  the  usual 
estimates  of  the  food  requirements  for  similar  occupations. 
In  a  considerable  proportion  of  these  balance  experiments 
the  subjects  were  found  to  be  too  far  out  of  nitrogen  equi- 
librium to  make  the  data  useful  from  our  present  point  of 
view.  The  results  of  nine  experiments,  in  which  the  fuel 
value  was  known  and  there  was  a  fairly  close  approach  to 
nitrogen  equilibrium,^  are  given  in  the  following  table,  which 

1  Neumann,  for  example,  in  35  days  on  insufficient  diet  lost  96  grams 
of  nitrogen  corresponding  to  600  grams  of  protein,  equivalent  to  about 
a. 5  kilograms  (5.5  pounds)  of  muscle  tissue. 

2  A  small  plus  balance  sufficient  to  cover  the  probable  loss  through 


PROTEIN   METABOLISM   AND   PROTEIN   REQUIREMENT      1 95 

shows  results  for  individual  subjects  whose  food  contained 
amounts  of  nitrogen  varying  from  40  to  72  grams  of  protein 
per  day :  — 

Total  Food,  Protein,  and  Nitrogen  Balance  per  Day 

(Chittenden) 


Subject 

Weight' 

Fuel  Value 

Protein 

Nitrogen  Balance 

kilograms 

calories 

grams 

grams 

c. 

57 

1613 

40.0 

+  0.165 

M. 

70 

2448 

53.2 

+  0.38 

U. 

61 

2068 

55.2 

+  0.158 

Be. 

61 

2152 

63.1 

+  0.34 

0.(1) 

64 

2509 

59-4 

+  0.509 

0.  (II) 

64 

2840 

53-9 

—  0.292 

Br. 

60 

2840 

54-2 

+  0.152 

D. 

62 

2450 

55-2 

+  0.089 

S. 

75 

2809 

71.7 

+  0.339 

As  Chittenden's  subjects  varied  considerably  in  size  and 
most  of  them  at  the  time  the  experiments  were  completed 
were  below  average  weight,  the  results  should  perhaps  be 
calculated  to  the  basis  of  a  man  weighing  70  kilograms  (154 
pounds)  for  comparison  with  each  other  and  with  other  data. 
On  this  basis  the  experiments  indicate  that  men  of  average 
weight  would  be  able  to  maintain  equilibrium  on  from  49 
to  72  grams  of  protein  per  day  under  the  conditions  of  these 
experiments. 

Chittenden  bases  his  estimate  of  the  protein  requirement, 

the  skin  is  quite  as  good  evidence  of  equilibrium  as  a  result  in  which  the 
nitrogen  of  the  food  is  exactly  balanced  by  that  of  the  feces  and  urine. 


196  CHEMISTRY   OF   FOOD   AND   NUTRITION 

not  only  upon  the  nitrogen  balances,  but  also  upon  the 
amounts  of  nitrogen  observed  to  be  eliminated  daily  through 
the  kidneys  over  long  periods  in  which  the  body  may  or  may 
not  have  been  in  complete  equilibrium,  but  in  which  health 
and  efficiency  were  certainly  maintained.  The  first  men  to 
serve  as  subjects  in  this  investigation  w^ere  Chittenden  him- 
self and  his  associates,  who  all  continued  their  professional 
work  and  either  reported  no  effect  or  felt  benefited  by  the 
change  to  the  low  protein  diet.  Similar  experiments  were 
then  made  upon  a  squad  of  soldiers,  who  during  the  test  were 
quartered  near  the  laboratory  and  were  given  regular  ex- 
ercise in  the  gymnasium  in  addition  to  their  light  duties 
about  their  quarters.  These  men  showed  marked  improve- 
ment in  physical  condition  during  the  test,  probably  due  in 
part  to  their  more  regular  habits  of  life  and  their  gymnastic 
instruction.  In  order  to  eliminate  this  factor  while  still 
applying  the  low  protein  diet  to  young  and  physically  active 
men,  the  investigation  was  extended  to  cover  a  group  of 
university  athletes  who  were  already  well  trained  and  in 
prime  physical  condition  at  the  beginning  of  the  dietary 
experiments.  These  athletes  not  only  maintained,  but  in 
many  cases  improved,  their  gymnastic  records  while  on  the 
low  protein  diet,  one  of  them  winning  an  all-round  gymnastic 
championship  during  the  time.  In  a  recent  summary  ^ 
Chittenden  states  that  his  data  "  are  seemingly  harmonious 
in  indicating  that  the  physiological  needs  of  the  body  are 
^Nutrition  of  Man,  pp.  226,  272. 


PROTEIN   METABOLISM  AND   PROTEIN   REQUIREMENT      1 97 

fully  met  by  a  metabolism  of  protein  matter  equal  to  an 
exchange  of  o.io  to  0.12  grams  of  nitrogen  per  kilogram  of 
body  weight  per  day,  provided  a  sufficient  amount  of  non- 
nitrogenous  foods  is  taken  to  meet  the  energy  requirements 
of  the  body."  This  would  correspond  to  44  to  53  grams  of 
protein  per  day  for  a  man  of  average  weight,  and  Chitten- 
den considers  that  for  such  a  man  an  allowance  of  60  grams 
of  protein  per  day  should  certainly  be  entirely  adequate. 

It  may  be  recalled  that  this  allowance  is  based  upon  ob- 
servations on  men,  some  of  whom  were  not  in  equilibrium 
and  all  of  whom  had  already  been  on  the  restricted  diet  for 
some  weeks  or  months  and  had  doubtless  lost  body  protein 
in  coming  to  this  low  level  of  protein  metabolism.  It  follows 
that  to  maintain  nitrogen  equilibrium  with  the  full  store  of 
protein  which  is  carried  on  an  ordinary  diet,  must  necessarily 
call  for  a  somewhat  larger  amount  of  protein  than  was  used 
in  Chittenden's  experiments,  probably  in  the  neighborhood 
of  75  grams  of  protein  per  man  per  day. 

INFLUENCE  OF  MUSCULAR  EXERCISE 

At  one  time  it  was  supposed  that  muscular  power  was 
generated  at  the  expense  of  muscle  substance,  and  this,  of 
course,  necessitated  the  belief  that  muscular  work  always 
increased  protein  katabolism.  Now  that  we  know  that  the 
muscles  work  quite  as  well  at  the  expense  of  carbohydrates 
and  fats  as  of  protein,  the  conclusion  that  muscular  work 
necessarily  increases  the  katabolism  of  protein  is  far  from 


1 98  CHEMISTRY    OF   FOOD   AND   NUTRITION 

inevitable.  It  is  only  necessary  to  observe  the  effects  of 
regular  muscular  exercise,  either  in  athletic  training  or  in 
normal  labor,  to  see  that  the  muscles  do  not  waste  away  when 
thus  used,  but  rather  tend  to  become  larger.  Such  a  growth 
of  the  muscles  tends  toward  a  storage  rather  than  a  loss  of 
protein.  Usually,  however,  muscular  work  also  results  in 
increased  appetite,  and  it  is  difficult  to  separate  the  effects 
of  the  exercise  from  those  of  the  extra  food. 

Whether  muscular  work  acts  directly  to  increase  the 
amount  of  protein  katabolized  in  the  body  can  only  be 
determined  by  experiments  in  which  sufficient  extra  fats  and 
carbohydrates  are  fed  to  furnish  the  extra  fuel  required  on 
the  working  days.  But  since  fats  and  carbohydrates  are 
"protein  sparers,"  the  feeding  of  these  in  any  excess  over 
just  what  is  necessary  to  provide  for  the  increased  energy 
requirement  would  tend  to  decrease  the  katabolism  of  pro- 
tein and  coimteract  any  effect  which  the  muscular  work 
might  otherwise  have  in  increasing  protein  katabolism. 
Hence,  in  order  to  show  conclusively  whether  muscular 
work  of  itself  has  any  influence  upon  the  protein  metabolism, 
it  would  be  necessary  to  determine  the  mechanical  efficiency 
of  the  man,  then  to  bring  him  into  equilibrium  with  aii 
amount  of  food  just  sufficient  for  his  needs,  and  finally  to 
have  him  perform  a  measured  amount  of  work  at  the  same 
time  adding  to  his  diet  an  amount  of  fats  and  carbohydrates 
just  sufficient  to  furnish  the  extra  energy  required  for  the 
work   performed.     Such    elaborate    experiments    have    not 


PROTEIN   METABOLISM  AND   PROTEIN   REQUIREMENT      1 99 

yet  been  made,  but  we  have  sufficient  data  to  show  that 
they  are  not  necessary  for  practical  purposes.  Many  ex- 
periments have  shown  conclusively  that  increased  work, 
when  accompanied  by  a  sufficient  increase  in  the  amount  of 
fats  and  carbohydrates  fed,  does  not  necessarily  increase  the 
katabolism  of  protein. 

The  following  data  from  Atwater  {Report  of  the  Storrs, 
Connecticut,  Agricultural  Experiment  Station  J  or  iQ02-igoj, 
page  127)  show  the  average  results  of  a  long  series  of 
rest  and  work  experiments  with  men  in  the  respiration 
calorimeter :  — 


Average  Metabolism  per  Day 

Nature  op  Experiment 

Per  Person 

Per  Kilogram 
Body  Weight 

Per  Square 
Meter  Surface 

Energy, 
calories 

Protein, 
grams 

Energy, 
calories 

Protein, 
grams 

Energy, 
calories 

Protein, 
grams 

Rest:  Food  generally  suffi- 
cient for  equilibrium ;   5 
subjects,  2  7  experiments, 
covering  82  days  .     .     . 

Work:    8   hours  per  day. 
Food  generally  not  quite 
sufficient  for  equilibrium  ; 
3    subjects,     24    experi- 
ments, covering  76  days . 

2310 
4556 

103.8 
108.I 

33-5 
62.9 

1.49 

1116 
2129 

50.1 
50.5 

Taking  account  of  the  small  difference  in  average  size, 
i.e.  comparing  the  figures  per  unit  of  weight  or  of  surface 


200  CHEMISTRY    OF    FOOD   AND    NUTRITION 

rather  than  per  person,  it  will  be  seen  that  muscular  work 
sufficient  to  nearly  double  the  energy  metabolism  had  no 
appreciable  effect  upon  the  amount  of  protein  metabolized. 
Considering  the  large  amount  of  exceptionally  accurate  re- 
search represented  in  these  average  figm-es,  they  seem  to 
justify  the  conclusion  that  if  muscular  work  has  any  tend- 
ency to  increase  the  "wear  and  tear"  of  muscle  substance, 
such  effect  is  normally  balanced  by  the  tendency  of  the 
muscles  to  grow  (and  therefore  store  protein)  when  exercised. 
Moreover,  it  is  certain  that  any  effect  which  muscular 
work  might  have  in  increasing  protein  metabolism  would 
be  very  much  less  than  its  effect  in  increasing  the  total 
metabolism.  If,  then,  starting  -wdth  a  diet  which  maintains 
protein  equiUbrium  at  rest,  the  total  food  is  increased  suffi- 
ciently to  pro\ade  for  the  muscular  work,  and  the  increase 
in  the  diet  is  accompUshed  by  adding  any  reasonable  com- 
bination of  food  materials,  we  may  feel  sure  that  these  will 
supply  plenty  of  protein  to  meet  any  possible  increase  in 
the  protein  requirement.  Hence,  in  planning  the  diet  of 
a  man  at  hard  muscular  work,  any  reasonable  combination 
of  foodstuffs  given  in  sufficient  abundance  to  meet  the  energy 
requirement  will  almost  certainly  supply  an  ample  amount 
of  protein. 


PROTEIN   METABOLISM   AND    PROTEIN    REQUIREMENT       20I 

PROTEIN  REQUIREMENT  IN   RELATION  TO  AGE 
AND    GROWTH 

If  a  man  at  moderately  active  work  takes  a  diet  which 
furnishes  3000  calories  and  75  grams  of  protein,  he  is  taking 
10  per  cent  of  his  calories  in  the  form  of  protein.  Of  course 
the  protein  requirement  cannot  bear  a  fixed  relation  to  the 
calorie  requirement,  since  the  latter  is  largely  influenced  by 
activity,  while  the  former  is  not.  Most  men,  when  at  com- 
plete rest,  would  require  more  than  10  per  cent  of  their  calories 
in  the  form  of  protein  because  the  lack  of  exercise  would  not 
reduce  the  protein  requirement  to  the  same  extent  as  the 
energy  requirement.  On  the  other  hand,  most  Americans 
are  accustomed  to  take  more  than  10  per  cent  of  their  calories 
as  protein  regardless  of  whether  they  require  it  or  not.  If, 
then,  the  active  man's  need  for  protein  is  met  by  supplying 
him  with  10  per  cent  of  his  needed  calories  in  the  form  of 
protein,  this  will  serve  as  a  convenient  starting  point  in  con- 
sidering the  requirements  of  a  child.  Let  this  be  compared 
with  the  normal  dietary  of  an  infant.  Human  milk  averages 
about  1.6  per  cent  protein,  4.0  per  cent  fat,  7.0  per  cent 
carbohydrate.  Here  about  9  per  cent  of  the  calories  are 
taken  in  the  form  of  protein,  or  about  the  same  proportion 
as  has  been  allowed  for  the  full-grown  active  man.  During 
the  suckling  period  the  growth  is  relatively  more  rapid  than 
at  any  other  age.     Mendel  ^  gives  the  following  figures :  — 

1  Childhood  and  Growth,  p.  18. 


202  CHEMISTRY    OF   FOOD    AND    NUTRITION 

The  Relative  Daily  Gain  in  Body  Weight  of  Children, 

In  the  first  month  is  about i.oo  per  cent 

At  the  middle  of  the  first  year    ....  0.30  per  cent 

At  the  end  of  the  first  year 0.15  per  cent 

At  the  fifth  year       0.03  per  cent 

Maximima  in  later  years 

for  boys 0.07  per  cent 

for  girls 0.04  per  cent 

If,  then,  the  full-grown  man  and  the  child  at  the  time  of 
most  rapid  growth  each  requires  but  10  per  cent  of  his  calories 
in  the  form  of  protein,  it  seems  probable  that  this  proportion 
is  also  sufficient  for  any  intermediate  age,  so  long  as  the  diet 
is  of  ample  fuel  value,  and  the  protein  of  a  kind  well  adapted 
for  conversion  into  body  tissue.  Just  as  the  child  requires 
more  calories  per  unit  of  weight  than  the  adult,  so  it  requires 
more  protein  per  unit  of  weight,  but  not  necessarily  a  diet 
richer  in  protein  in  the  usual  sense  of  containing  a  larger 
proportion  of  protein  to  total  food. 

Since  the  relative  rate  of  growth  is  so  much  greater  during 
the  suckling  period  than  at  any  later  time,  it  would  be  un- 
reasonable to  suppose  that  the  demands  of  growth  would 
at  any  time  call  for  a  diet  richer  in  protein  (relatively  to 
calories)  than  human  milk,  though  for  other  reasons  it  is 
decidedly  advisable  to  feed  children  during  the  first  year  or 
two  after  weaning  very  largely  upon  cow's  milk,  which  fur- 
nishes about  19  per  cent  of  its  calories  in  the  form  of  protein. 
Such  a  surplus  of  protein  in  the  dietary  of  a  child,  while  not 


PROTEIN  METABOLISM   AND   PROTEIN   REQUIREMENT      203 

strictly  necessary,  cannot  be  regarded  as  objectionable  if 
taken  in  the  form  of  milk.  The  kind  of  protein  for  children's 
dietaries  is  of  great  importance,  since  under  favorable  con- 
ditions the  growth  may  be  such  as  to  call  for  a  conversion  of 
30  to  40  per  cent  of  the  food  protein  into  body  material. 
Ordinarily  it  is  best  to  use  milk  as  the  main  source  of  protein 
throughout  the  whole  of  infancy  and  early  childhood.  Young 
and  middle-aged  people  usually  utilize  quantities  of  protein 
considerably  greater  than  they  require.  The  arguments 
for  and  against  such  a  surplus  of  protein  in  the  diet  will  be 
reviewed  briefly  in  the  next  chapter;  at  present  we  are 
concerned  with  the  effect  of  age  rather  than  the  general 
question  of  high  or  low  protein  diet. 

Elderly  people  show  both  a  diminished  protein  require- 
ment and  a  diminished  power  of  dealing  with  excess.  Sur- 
plus protein  taken  in  the  food  is  not  so  rapidly  absorbed 
and  katabolized,  and,  while  there  appears  to  be  no  essential 
difference  in  the  form  in  which  the  nitrogen  is  finally  ex- 
creted, the  susceptibility  to  excessive  putrefaction  of  protein 
appears  to  be  increased.  It  would  seem  that  in  the  dietary  of 
the  aged  the  protein  should  be  reduced  to  at  least  as  great 
an  extent  as  are  the  calories. 

REFERENCES 

Atwater  and  Benedict.  Comparison  of  Fats  and  Carbohydrates  as 
Protectors  of  Body  Material.  Bull.  136,  (pp.  176-187).  Office  of 
Experiment  Stations,  U.  S.  Dept.  Agriculture. 


204  CHEMISTRY    OF   FOOD    AND    NUTRITION 

Benedict.     The  Influence  of  Inanition  on  Metabolism.     Publication 

No.  77,  Carnegie  Institution  of  Washington. 
Chittenden.     Physiological  Economy  in  Nutrition. 

The  Nutrition  of  Man. 

Hammarsten.     Textbook  of  Physiological  Chemistry. 

LusK.     Elements  of  the  Science  of  Nutrition. 

SiVEN.     [On  Protein  Requirement.]    Skandinavisches  Archiv  f.  Physiolo- 

gie,  lo,  91 ;  II,  308. 
Von  Noorden.    Metabolism  and  Practical  Medicine,  Vol.  I,  pp.  283- 

383- 


CHAPTER  VIII 
FOOD   HABITS   AND   DIETARY   STANDARDS 

Having  considered  in  the  last  two  chapters  the  need  of 
the  body  for  food,  in  terms  of  calories  and  of  protein,  we 
may  now  inquire  how  the  food  requirements  thus  determined 
compare  with  actual  food  habits  and  what  should  be  the 
standard  of  a  desirable  diet,  both  as  to  total  food  and  pro- 
portional amounts  of  the  different  foodstuffs. 

The  earliest  attempts  to  set  dietary  standards  in  terms 
of  nutrients  were  those  of  the  German  physiologists,  among 
which  the  most  authoritative  and  influential  was  that  of 
Voit.  Voit  suggested  as  a  proper  allowance  of  foodstuffs 
for  a  man  at  moderate  muscular  work :  — 

Protein,  ii8  grams. 

Fat,  56  grams. 

Carbohydrates,  500  grams. 

This  dietary  would  have  a  fuel  value  of  approximately  3000 
calories.  The  allowance  of  118  grams  of  protein,  which  has 
since  provoked  considerable  discussion,  is  said  to  have  been 
based  upon  the  average  protein  metabolism  of  many  labor- 
ing men  who  were  living  apparently  upon  unrestricted  diet, 
so  that  it  was  practically  the  result  of  dietary  study.  In 
the  division  of  the  remaining  calories  between  fat  and  car- 

205 


2o6  CHEMISTRY    OF   FOOD    AND   NUTRITION 

bohydrate,  Voit  made  the  allowance  of  fat  low  and  of  car- 
bohydrates high  in  order  to  cheapen  the  dietary. 

Playfair,  in  England,  recommended  as  a  standard  for  a  man 
at  moderate  work :  — 

Protein,  119  grams. 

Fat,  51  grams. 

Carbohydrate,  531  grams. 

This  would  yield  3060  calories  and  is  evidently  based  quite 

directly  upon  Voit's  recommendations. 

In  France,  Gautier  has  proposed  as  a  standard  for  men 

with  little  muscular  work :  — 

Protein,  107  grams. 

Fat,  65  grams. 

Carbohydrate,  407  grams. 

This  allowance  of  nutrients  —  which  is  based  in  part  upon 

carbon   and   nitrogen   balance   experiments,   in   part   upon 

studies  of  French  families  selected  as  typical,  and  in  part 

upon  the  statistics  of  food  consumed  in  Paris  for  a  period 

of  ten  years  —  would  supply  2630  calories. 

In  America  dietary  standards  have  been  discussed  chiefly 

by   Atwater,    Chittenden,  and    Langworthy.    Atwater,    in 

his  later  writings,^  ceasing  to  make  distinction  between  fats 

and  carbohydrates  as  sources  of  energy  in  ordinary  dietaries, 

but  making  allowances  for  different  degrees  of  muscular 

activity,  recommended  the  following  standards :  — 

^  Farmer's  Bulletin  No.  142,  U.  S.  Department  of  Agriculture.  Also 
Fifteenth  Annual  Report  Agricultural  Experiment  Station,  Storrs,  Conn., 
1903. 


FOOD    HABITS    AND    DIETARY    STANDARDS 


207 


Fuel  Value, 
Calories 


Man  with  hard  muscular  work    .... 

Man  with  moderately  active  muscular  work 

Man  at  sedentary  or  woman  with  moder- 
ately active  work 

Man  without  muscular  exercise  or  woman 
at  light  to  moderate  work 


4150 
3400 

2700 

2450 


That  these  standards  were  not  intended  simply  as  ex- 
pressions of  the  actual  needs  of  the  body  is  plainly  shown 
by  the  allowance  of  150  grams  of  protein  for  a  man  at  hard 
work,  as  against  100  grams  for  a  sedentary  man.  By  his 
own  experiments  with  men  at  rest  and  at  work  in  the  res- 
piration calorimeter  Atwater  had  demonstrated,  as  shown 
in  the  preceding  chapter,  that  muscular  work  need  not  in- 
crease protein  metabolism  if  a  sufficient  amount  of  fuel  be 
provided  in  the  form  of  carbohydrates  and  fats.  Hence, 
when,  in  providing  for  muscular  work,  he  proposes  to  in- 
crease the  protein  in  practically  the  same  ratio  as  the  calories, 
the  idea  evidently  is  not  that  such  an  increase  is  necessary, 
but  simply  that  it  was  considered  advisable  on  general  grounds 
not  to  alter  very  greatly  the  nature  of  the  diet  in  increasing 
its  amount. 

In  explanation  of  the  liberality  of  his  standards  Atwater 
suggested  that  "the  standard  must  vary  not  only  with  the 
conditions  of  activity  and  environment,  but  also  with  the 
nutritive  plane  at  which  the  body  is  to  be  maintained.    A 


208 


CHEMISTRY    OF    FOOD    AND   NUTRITION 


man  may  live  and  work  and  maintain  bodily  equilibrium  on 
either  a  higher  or  a  lower  nitrogen  level,  or  energy  level. 
One  essential  question  is,  What  level  is  most  advantageous  ? 
The  answer  to  this  must  be  sought,  not  simply  in  metabolism 
experiments  and  dietary  studies,  but  also  in  broader  observa- 
tions regarding  bodily  and  mental  efficiency  and  general 
health,  strength,  and  welfare." 

Langworthy,  maintaining  a  similar  point  of  view,  has 
collected  the  data  of  large  numbers  of  dietaries  believed  to 
be  fairly  representative  of  the  food  habits  of  people  of  dif- 
ferent occupations  in  the  United  vStates  and  other  countries, 
and  stated  them  in  terms  of  protein  and  calories  per  man  per 
day  wdth  the  following  results:  — 

Langworthy's  Compilation  of  Results  of  Dietary  Studies 


Occupation  of  Head  of  Family 

Food  per  Man  ^ 
PER  Day 

Protein, 
grams 

Fuel  value, 
calories 

United  States : 

Man  at  very  hard  work  (average  19  studies)  .     . 
Farmers,  mechanics,  etc.  (average  162  studies)  . 
Business  men,  students,  etc.  (average  51  studies) 
Tnraates  of  institutions,  little  or  no  muscular  work 

(average  of  49  studies) 

Very  poor  people,  usually  out  of  work  (average  of 

15  studies) 

Canada:  Factory  hands  (average  13  studies)      .     . 

177 
100 
106 

86 

69 
108 

6000 
3425 
3285 

2600 

2100 

3480 

^  As  explained  in  Chapter  VI,  it  is  assumed  that  women  consume  0.8 
as  much  food  as  men,  and  children  of  different  ages  from  0.3  to  0.8  as 
much  as  the  man  of  the  family. 


FOOD    HABITS    AND   DIETARY    STANDARDS 


209 


Occupation  of  Head  of  Family 


England :  Workingmen  .     .     .     . 
Scotland :  Workingmen       ,     .     , 
Ireland :  Workingmen   ... 
Germany:  Workingmen     .     . 

Professional  men  .... 
France  :  Men  at  light  work  . 
Japan :  Laborers 

Professional  and  business  men 

China :  Laborers 

Egypt :  Native  laborers     .     . 
Congo :  Native  laborers     .     . 


Food  per  Man 

PER 

Day 

Protein, 

Fuel  value, 

grams 

calories 

89 

2685 

108 

3228 

98 

3107 

134 

3061 

III 

2511 

IIO 

2750 

118 

4415 

87 

2190 

91 

3400 

112 

2825 

108 

2812 

Langworthy  states  that,  while  the  figures  given  for  Ameri- 
can dietaries  are  averages  of  available  data,  general  aver- 
ages were  not  available  for  other  countries,  and  it  was  nec- 
essary to  choose  such  studies  as  seemed  similar  in  purpose  and 
method  to  the  American  work  and  which,  so  far  as  could  be 
judged,  represented  usual  and  normal  rather  than  abnormal 
or  experimental  conditions.  He  concludes  that  the  results 
obtained,  the  world  over,  for  persons  of  moderate  activity, 
''do  not  differ  very  markedly  from  a  general  average  of  100 
grams  of  protein  and  3000  calories  of  energy,  and  that  it  is 
fair  to  say  that,  although  foods  may  differ  very  decidedly, 
the  nutritive  value  of  the  diet  in  different  regions  and  under 
different  circumstances  is  very  much  the  same  for  a  like 
amount  of  muscular  work."    Langworthy  points  out  that  in 


2IO  CHEMISTRY    OF   FOOD    AND    NUTRITION 

some  cases  this  may  not  be  apparent  until  allowance  is  made 
for  differences  in  body  weight.  Thus  he  estimates  the  aver- 
age weight  of  the  Japanese  professional  and  business  men  at 
105  pounds,  so  that  their  food  consumption  of  87  grams 
protein  and  2190  calories  corresponds  to  105  grams  protein 
and  3120  calories  for  a  man  of  150  pounds,  which  agrees  well 
with  the  American  average  for  similar  employment. 

As  a  standard  for  men  with  more  muscular  activity,  such 
as  mechanics  at  moderately  active  work,  Langworthy  sug- 
gests :  — 

For  food  purchased,  115  grams  protein;  3800  calories. 
For  food  eaten,  105  grams  protein;  3500  calories. 

Chittenden  differs  from  those  whose  standards  have  been 
quoted  in  giving  almost  no  weight  to  the  results  of  dietary 
studies,  holding  that  these  serve  chiefly  as  a  measure  of  self- 
indulgence,  and  that  the  true  measure  of  what  the  body  will 
most  profitably  use  is  to  be  found  in  the  results  of  experi- 
ments upon  the  protein  metabolism,  such  as  have  been  de- 
scribed in  the  preceding  chapter.  On  the  basis  of  these  ex- 
periments he  proposes  as  a  standard  allowance  for  the  man 
of  70  kilograms  body  weight,  60  grams  of  protein  and  2800 
calories  per  day.  For  business  and  professional  men  such  as 
Chittenden  evidently  has  in  mind,  the  allowance  of  2800 
calories  is  in  substantial  agreement  -vsath  earlier  estimates. 
Sixty  grams  of  protein  for  a  man  of  70  kilograms  is,  however, 
decidedly  lower  than  any  standard  previously  current. 

In  order  to  afford  a  concrete  comparison  there  are  given 


FOOD    HABITS    AND    DIETARY    STANDARDS 


211 


below  (i)  a  dietary  arranged  to  agree  with  the  Atwater 
standard,  (2)  a  dietary  suggested  by  Chittenden  in  his  Nu- 
trition of  Man. 

Example  of  Dietary  for  Business  Man  Based  on  Atwater 
Standards 


Articles  of  Food 


Breakfast : 

Bananas 

Oatmeal  (weighed  dry) 

Sugar  

Cream 

Eggs  (2) 

Toast 

Roll 

Butter 

Luncheon : 

Bluefish    

Potato 

Rolls 

Butter 

Milk 

Apple  pie 

Dinner: 

Steak 

Potatoes 

Corn,  canned     .     .     . 

Celery 

Bread 

Butter 

Baked  apple       .     .     . 
Cream 

Total 


Weight 

OF  Food 

Ounces 

Grams 

3-5 

100 

I.O 

28 

I.O 

28 

2.0 

56.5 

3-5 

100 

2.0 

56.6 

I.O 

28 

o.S 

14 

4.0 

113 

4.2 

120 

2.0 

56.5 

I.O 

28 

5-0 

142 

4.0 

113 

4.0 

113 

4.0 

113 

3-5 

100 

4.0 

113 

2.0 

56.5 

I.O 

28 

5-5 

155 

4.0 

113 

Fuel  Value 


Calories 


100 
III 
III 
IIO 

150 
200 

75 
100 

100 
100 
150 
200 
100 
300 

200 

95 
100 

20 
150 
200 
100 
220 


2992 


Protein 


Calories     Grams 


5-2 

18.7 
5.6 

54-0 

28.0 

10.6 

0.5 

88.0 
10.5 
21.2 

I.O 

19.0 
15.0 

108.0 

lO.O 
12.2 

6.0 
21.2 

I.O 

2.5 
II. 2 


1-3 
4-7 

1.4 

135 

7.0 
2.7 
0.1 

22.0 
2.6 

5-3 
0.2 
4.8 
3-8 

27.0 
2.5 
3-0 
1-5 
5-3 
0.2 
0.6 
2.8 


112.3 


212 


CHEMISTRY    OF   FOOD    AND    NUTRITION 


Chittenden's  Suggested  Dietary  for  Man  of  Average  Weight 
(From  The  Nutrition  of  Man) 


Articles  of  Food 


Weight 


Grams 


Fuel  Value 


Calories 


Protein 


Grams 


Breakfast : 

One  shredded  wheat  biscuit 

One  teacup  of  cream 

One  German  water  roll 

Two  I -inch  cubes  of  butter 

Three  fourths  cup  of  coffee 

One  fourth  teacup  of  cream 

One  lump  of  sugar 

Lunch : 
One  teacup  homemade  chicken  soup      .     . 

One  Parker-house  roll 

Two  I -inch  cubes  of  butter 

One  slice  lean  bacon 

One  small  baked  potato  (about  2  ounces)  . 

One  rice  croquette 

Two  oimces  of  maple  syrup 

One  cup  of  tea  with  one  slice  lemon  .     .     , 
One  lump  of  sugar 

Dinner: 
One  teacup  cream-of-com  soup    .... 

One  Parker-house  roll 

One  inch  cube  of  butter 

One  small  lamb  chop,  broiled  lean  meat  .     . 

One  teacup  of  mashed  potato 

Apple-celery-lettuce  salad  with  Mayonnaise 

dressing 

One  Boston  cracker,  split 

One  half  teacup  of  bread  pudding  .... 
One  half-inch  cube  American  cheese       .     . 

One  denii-t^sse  coffee 

One  lump  of  sugar 

Total 


30 
120 

57 

38 

100 

30 
10 


144 
38 
38 
10 
60 
90 
60 

10 


130 
38 
19 
30 

167 

50 
12 

85 


106 
206 

165 

284 

51 
38 

60 
no 
284 
65 
55 
150 
166 

38 

72 
no 
142 

92 
175 

75 

47 

150 

50 

38 


315 
3.12 

5-07 
0.38 
0.26 
0.78 


5.2s 
3.38 
0.38 
2.14 

1-53 
3-42 


3.25 
338 
0.19 
8.51 
3-34 

0.62 
1.32 
5-25 
3-35 


2729 


58.07 


FOOD    HABITS    AND    DIETARY    STANDARDS  213 

The  general  impression  that  equally  competent  authorities 
differ  widely  in  their  estimates  of  the  desirable  amount  of  food 
seems  to  call  for  some  consideration  of  the  apparent  dis- 
crepancies between  standards  which  have  been  proposed. 

STANDARDS   FOR  FUEL  VALUE 

It  has  been  shown  in  a  previous  chapter  that  different 
normal  individuals  of  similar  age  and  physique  are  substan- 
tially alike  in  their  energy  requirement  when  performing 
equivalent  amounts  of  muscular  work,  and  that  it  is  primarily 
the  muscular  activity,  and  not  personal  idiosyncrasy  or  the 
amount  of  food  eaten,  which  determines  the  amount  of  energy 
transformed  in  the  body.  A  dietary  standard  of  high  fuel 
value,  and  designed  to  maintain  metabolism  on  a  high  energy 
level  provides,  therefore,  primarily  for  a  large  amount  of 
muscular  work.  If  this  work  is  not  performed  and  the  food 
continues  to  be  eaten  and  digested,  we  may  expect  to  find  a 
storage  of  fuel  in  the  body  chiefly  in  the  form  of  fat,  and  this 
is  true  whether  the  surplus  food  eaten  is  carbohydrate,  fat, 
or  protein.  Thus  the  store  of  body  fat  which  a  person  carries 
is  the  most  reliable  indication  as  to  whether  the  amount  of 
food  habitually  eaten  is  or  is  not  properly  adjusted  to  the  work 
performed.  The  storage  of  fat  does,  however,  in  itself  modify 
the  food  requirement.  While  it  is  true,  as  has  been  shown, 
that,  as  between  a  lean  and  a  fat  man  having  the  same  weight, 
the  lean  man  will  have  the  greater  food  requirement,  yet  it  is 
also  true  that  when  any  given  man  becomes  fat,  his  increased 


214  CHEMISTRY    OF    FOOD    AND    NUTRITION 

size  of  body  calls  for  increased  metabolism  of  energy.  The 
work  involved  in  walking,  for  example,  will  increase  in  pro- 
portion to  the  weight  moved  {i.e.  to  the  weight  of  the  body  as 
a  whole) ;  and  the  work  of  respiration  will  increase  about  in 
proportion  to  the  weight  of  that  part  of  the  body  which  must 
be  moved  w^th  the  expansion  and  contraction  of  the  lungs ; 
while,  if  fat  is  deposited  in  such  a  way  as  to  interfere  directly 
with  the  free  play  of  the  muscles,  there  may  be  an  actual  low- 
ering of  muscular  efficiency,  so  that  a  larger  expenditure  of 
energy  may  be  required  in  order  to  produce  a  given  amount  of 
work.  If  the  liberal  diet  is  continued  and  the  digestion  re- 
mains normal,  the  storage  of  fat  wall  continue  until  it  raises 
the  energy  expenditure  of  the  body  to  a  point  where  the  food 
is  no  longer  in  excess.  If  the  store  of  fat  carried  when  this 
point  is  reached  is  excessive,  the  fuel  value  has  been  too  high ; 
if  the  store  of  fat  is  not  excessive,  the  fuel  value  of  the  diet, 
although  greater  than  would  have  been  necessary  to  maintain 
the  body  at  its  former  weight,  has  not  been  too  high,  and  the 
body  has  acquired  an  asset  whose  utility  may  not  always  be 
recognized  in  health,  but  which  may  be  of  great  value  in  case 
of  accident,  illness,  exposure,  or  any  unusual  strain. 

Opinions  differ  as  to  the  desirable  degree  of  fatness  as  in- 
dicated by  the  relation  of  height  to  body  weight. 

According  to  Hagler,^  the  insurance  company  at  Basel  is 
very  cautious  in  its  dealings  "vv-ith  individuals  of  less  than  340 
grams  or  more  than  530  grams  of  weight  per  centimeter  of 
*  Cabot's  Diseases  of  Metabolism,  p.  158. 


FOOD   HABITS   AND    DIETARY    STANDARDS  21 5 

body  height,  and  such  are  usually  rejected.  In  English  units 
this  rule  would  require  the  weight  to  be  between  1.90  and 
2.97  pounds  to  the  inch.  For  a  height  of  5  feet  8  inches 
this  would  mean  a  range  of  body  weight  from  130  to  202 
pounds. 

Hill  ^  estimates  the  average  height  at  25  years  of  age  as 
5  feet  3  inches  for  women  and  5  feet  8  inches  for  men,  and  the 
corresponding  average  weights  as  119  and  150  pounds  respec- 
tively. He  considers  that  variations  of  10  to  15  per  cent  above 
or  below  the  average  should  be  considered  normal.  According 
to  this  estimate  the  woman  of  5  feet  3  inches  should  weigh 
not  less  than  102-107,  nor  more  than  131-136  pounds,  and  the 
man  of  5  feet  8  inches  not  less  than  128-135,  nor  more  than 
1 6 5-1 73  pounds.  These  figures  are  exclusive  of  clothing.  Hill 
considers  as  "fat"  those  persons  whose  weight  exceeds  the 
average  by  15  to  30  per  cent,  and  as  "over  fat"  those  who 
exceed  by  more  than  30  per  cent,  i.e.  over  155  pounds  for  a 
woman  5  feet  3  inches  or  over  195  pounds  for  a  man  5  feet 
8  inches. 

The  Basel  life  insurance  company  would  thus  accept  persons 
whom  Hill  regards  as  over  fat  and  would  exclude  as  being  too 
thin  some  of  those  whom  Hill  regards  as  normal. 

Recently  Symonds  has  published  ^  the  average  relation  of 
height  to  weight  in  both  men  and  women  at  different  ages,  as 

^  Recent  Advances  in  Physiology  and  Biochemistry. 
2  Medical  Record,  Sept.  5,  1908  ;   and  McClure's  Magazine,  January, 
1909. 


2l6 


CHEMISTRY    OF    FOOD    AND   NUTRITION 


computed  from  the  records  of  accepted  applicants  for  life 
insurance  in  the  United  States  and  Canada.  The  results  are 
found  in  the  following  tables ;  that  for  men  being  based  on 
74,162  and  that  for  women  on  58,855  cases.  In  all  these  cases 
the  height  includes  shoes  and  the  weight  includes  ordinary- 
clothing. 


Symonds's  Table  of  Height  and  Weight  for  Men  at  Different 

Ages 

BASED    ON    74,162    accepted   APPLICANTS   FOR   LIFE   INSURANCE 

{Medical  Record) 


Ages 

15-24 

25-29 

30-34 

35-39 

40-44 

45-49 

50-54 

55-59 

60-64 

65-69 

Sft.  oin. 

120 

125 

128 

131 

133 

134 

134 

134 

131 

I  in. 

122 

126 

129 

131 

134 

136 

136 

136 

134 

2  in. 

124 

128 

131 

133 

136 

138 

138 

138 

137 

3  m. 

127 

131 

134 

136 

139 

141 

141 

141 

140 

140 

4  m. 

131 

135 

138 

140 

143 

144 

I4S 

145 

144 

143 

5  m. 

134 

138 

141 

143 

146 

147 

149 

149 

148 

147 

6  in. 

138 

142 

145 

147 

ISO 

151 

153 

IS3 

153 

iSi 

7  in. 

142 

147 

ISO 

152 

iSS 

iS6 

iS8 

158 

iS8 

iS6 

Sin. 

146 

151 

154 

157 

160 

161 

163 

163 

163 

162 

9  in. 

150 

155 

159 

162 

165 

166 

167 

168 

168 

168 

10  m. 

154 

159 

164 

167 

170 

171 

172 

173 

174 

174 

II  in. 

159 

164 

169 

173 

I7S 

177 

177 

178 

180 

180 

6  ft.  0  in. 

165 

170 

175 

179 

180 

183 

182 

183 

i8s 

i8s 

I  in. 

170 

177 

181 

185 

186 

189 

188 

189 

189 

189 

2  in. 

176 

184 

188 

192 

194 

196 

194 

194 

192 

192 

3  in. 

181 

190 

195 

200 

203 

204 

201 

198 

FOOD    HABITS    AND    DIETARY    STANDARDS 


217 


Symonds's  Table  of  Height  and  Weight  for  Women  at  Different 

Ages 

based  on  58,855  accepted  applicants  for  life  insurance 
{McClure's  Magazine)  . 


Ages 

15-19 

20-24 

25-29 

30-34 

35-39 

40-44 

45-49 

50-54 

55-59 

60-64 

4 

ft.  II  in. 

III 

113 

115 

117 

119 

122 

125 

128 

128 

126 

5 

ft.  0  in. 

113 

114 

117 

119 

122 

125 

128 

130 

131 

129 

I  in. 

115 

116 

118 

121 

124 

128 

131 

133 

134 

132 

2  in. 

117 

118 

120 

123 

127 

132 

134 

137 

137 

136 

3  in. 

120 

122 

124 

127 

131 

135 

138 

141 

141 

140 

4  in. 

123 

125 

127 

130 

134 

138 

142 

145 

145 

144 

sin. 

125 

128 

131 

135 

139 

143 

147 

149 

149 

148 

6  in. 

128 

132 

135 

137 

143 

146 

151 

153 

153 

152 

7  in. 

132 

135 

139 

143 

147 

150 

154 

157 

156 

155 

Sin. 

136 

140 

143 

147 

151 

155 

158 

161 

161 

160 

9  in. 

140 

144 

147 

151 

155 

159 

163 

166 

166 

i6s 

10  in. 

144 

147 

151 

155 

159 

163 

167 

170 

170 

169 

From  a  study  of  the  records  of  body  weight  in  relation  to 
the  mortahty  records  Symonds  concludes  that  among  young 
people  the  greatest  vitality  coincides  with  a  weight  somewhat 
above  the  accepted  average,  while  with  middle-aged  and 
elderly  people  a  condition  of  slightly  less  than  average  fatness 
is  most  favorable  to  vitality  and  longevity.  Another  way  of 
stating  the  same  facts  is :  That  the  average  of  healthy  men 
and  women  keep  themselves  sHghtly  too  thin  while  young, 
and  allow  themselves  to  grow  slightly  too  stout  as  they  grow 
older. 

Evidently,  however,  the  optimum  is  very  near  the  average 


2l8  CHEMISTRY    OF   FOOD    AND    NUTRITION 

of  the  accepted  applicants  as  shown  in  the  tables,  and  Symonds 
uses  these  figures  as  standards  in  his  computations  and  dis- 
cussions of  the  influence  of  overweight  and  underweight  on 
longevity  and  on  mortality  from  specific  diseases.  Symonds's 
data  therefore  support  the  opinion  that  the  average  degree  of 
fatness  of  healthy  American  people  is  just  about  the  most 
advantageous  fatness  for  them  to  maintain.  Whatever  we 
accept  as  the  ideal  relation  of  weight  to  height,  it  is  obvious 
that  the  proper  standard  for  fuel  value  of  the  diet  is.  that  which 
will  preserve  the  desired  degree  of  fatness  while  sustaining  the 
desired  amount  of  activity.  If  good  authorities  differ  in 
standards  for  fuel  value,  it  is  because,  consciously  or  uncon- 
sciously, they  contemplate  different '  amoimts  of  muscular 
activity  or  the  maintenance  of  a  different  physique. 

The  Appetite  as  a  Dietary  Standard. — It  is  sometimes  asked 
whether  a  normal  appetite  does  not  indicate,  as  well  as  can 
any  dietary  standard,  the  amount  of  food  which  is  desirable 
for  the  individual  in  the  given  circumstances. 

If  by  following  the  appetite  one  becomes  unduly  stout, 
or  is  visited  by  digestive  disturbances  which  are  an  obvious 
effort  on  the  part  of  the  body  to  free  itself  of  a  part  of  the  food 
eaten,  or,  on  the  other  hand,  if  one  becomes  unduly  thin,  or 
does  not  get  sufficient  fuel  to  support  a  full  day's  work,  it  is 
certain  that  some  standard  other  than  that  of  appetite  would 
be  of  decided  advantage.  But  if  from  year  to  year  the  body 
keeps  in  good  condition  for  its  work  and -maintains  a  fairly 
constant  weight,  which  bears  such  a  proportion  to  the  height 


FOOD   HABITS   AND   DIETARY    STANDARDS  219 

as  to  show  that  a  desirable  store  of  fat  is  being  carried,  it  is 
reasonably  certain  that  the  amount  of  food  eaten  in  the  course 
of  the  year  is  substantially  that  which  is  suited  to  the  degree 
of  activity  maintained;  and,  while  it  is  possible  that  still  fur- 
ther benefits  might  accrue  from  a  different  selection  of  food 
materials,  it  is  not  likely  that  any  advantage  could  result 
from  a  material  change  in  the  amount  (fuel  value)  of  food  con- 
sumed. Especially  is  it  in  the  highest  degree  improbable 
that  in  such  a  case  the  same  work  could  be  done  and  the  same 
weight  maintained  on  food  of  much  lower  .fuel  value,  however 
selected,  prepared,  or  eaten. 

It  is  of  interest  to  note  that  a  well-ordered  appetite  may  not 
only  serve  as  an  indication  of  the  amounts  of  food  needed 
over  long  periods  and  under  different  conditions  of  activity, 
»but  also  when  the  conditions  of  Hfe  are  fairly  uniform  may  be 
highly  efficient  in  determining  a  regular  intake  of  calories 
from  day  to  day.  Thus,  a  healthy  young  woman  living  on 
unrestricted  diet  with  menus  varied  daily  and  eating  simply 
according  to  appetite  was  found  to  take  on  five  successive 
days  2140,  2025,  2040,  2250,  2255  calories  respectively. 

STANDARDS   FOR  PROTEIN 

In  attempting  to  set  a  standard  for  the  amount  of  protein  in 
the  dietary  we  find  no  such  definite  and  satisfactory  basis  for 
judgment  as  in  the  case  of  total  food  (or  fuel)  value.  There  is 
no  indication  that  any  kind  of  work  necessarily  increases  the 
expenditure  of  protein  as  muscular  work  increases  the  ex- 


220  CHEMISTRY    OF    FOOD    AND    NUTRITION 

penditure  of  fuel,  and  the  body  cannot  store  up  protein  to 
anything  like  the  extent  that  it  stores  fuel  in  the  form  of  fat; 
the  feeding  of  protein  above  what  is  required  for  maintenance 
increases  only  slightly  the  store  of  protein  which  the  body 
carries. 

When  one  writer  proposes  an  amount  of  protein  but  little 
above  the  minimum  required  for  equilibrium,  while  another 
advocates  a  much  larger  amount,  there  is  implied  a  difference 
of  view  regarding  protein  such  as  no  longer  exists  with  respect 
to  the  energy  metaboHsm.  The  difference,  it  is  true,  is  hardly 
so  great  as  might  appear  from  a  casual  examination  of  the 
proposed  standards.  It  may  perhaps  be  most  fairly  ex- 
pressed in  terms  of  the  relation  between  protein  and  energy 
in  the  different  standards.  Protein  would  contribute,  accord- 
ing to  the  standards  of  Voit,  Playfair,  and  Gautier,  about  i6 
per  cent  of  the  fuel  value  of  the  food;  of  Atwater,  about 
1 5  per  cent ;  of  Langworthy,  1 2  per  cent ;  of  Chittenden,  Si 
per  cent. 

It  will  be  of  interest  to  examine  some  of  the  argimients 
which  have  been  advanced  in  favor  of  a  high  protein  or  of  a 
low  protein  diet.  The  following  extracts  are  given  in  chrono- 
logical order.  References  for  more  detailed  reading  are  given 
at  the  end  of  the  chapter,  arranged,  as  usual,  alphabetically 
by  authors,  though  if  several  are  to  be  read  they  may  best  be 
taken  up  chronologically. 


food  habits  and  dietary  standards         221 

Opinions  regarding  the    Value  of  Liberal  Protein 

Diet 

Liebig  believed  that  fats  and  carbohydrates  were  burned  in 
the  body  primarily  to  supply  it  with  warmth,  and  that  protein 
alone  sei-ved  as  the  source  of  muscular  work  and  other  forms  of 
tissue  activity.  He  therefore  classed  the  non-nitrogenous  as 
"respiratory"  and  the  nitrogenous  as  "plastic"  foodstuffs,  and 
treated  the  proteins  as  playing  a  "nobler"  part  in  nutrition  than 
can  be  taken  by  fat  or  carbohydrate.  Although  it  was  soon 
demonstrated  that  carbohydrates  and  fats  as  well  as  protein 
serve  the  body  in  the  production  of  muscular  energy,  yet  the 
influence  of  Liebig's  teaching,  and  of  the  great  attention  given 
to  protein  in  Voit's  classical  researches  on  nutrition,  together 
with  the  fact  that  protein  is  the  most  prominent  constituent  of 
protoplasm,  has  resulted  in  a  strong  tendency  to  associate  high 
protein  feeding  with  increased  stamina  and  muscular  power. 

The  reasoning  of  those  who  appreciated  the  results  of  more 
recent  experimental  work,  and  yet  believed  the  general  attitude 
of  Liebig  and  Voit  to  have  been  largely  sustained  by  experience, 
is  well  expressed  by  Von  Noorden,  who  wrote  in  1893  :  ^  — 

"When  one  considers  that  the  dietary  habits  of  peoples  are 
the  results  of  biological  laws,  it  would  seem  that  the  action  of 
these  laws,  extending  through  the  thousands  of  years  of  existence 
of  the  species,  would  have  resulted  in  the  establishment  of  suitable 
habits  regarding  the  amounts  of  protein  consumed.  The  data 
gathered  by  Voit  may  be  taken  as  showing  that  this  normal  habit 
involves  the  consumption  of  about  105  grams  of  digestible  pro- 
tein ^  per  day,  a  smaller  protein  consumption  being  usually  asso- 

1  Freely  translated  from  the  first  edition  of  Von  Noorden's  Pathologie 
der  Stofwechsel. 

^  Corresponding  to  Voit's  allowance  of  118  grams  of  total  protein  when 
the  food  for  the  sake  of  economy,  as  contemplated  by  Voit,  is  taken  some- 
what largely  from  vegetable  sources. 


222  CHEMISTRY    OF    FOOD    AND    NUTRITION 

dated  with  weak  individuals  or  inactive  peoples.  WTiile  men 
can  maintain  equilibrium  on  less,  still  it  can  rightly  be  said  that 
a  Hberal  protein  consumption  makes  for  a  full  development  of 
the  man.  A  single  individual  may  for  years,  or  even  decades, 
offend  against  this  biological  law  unpunished.  WTien,  however, 
the  small  consumption  of  protein  continues  for  generations,  there 
results  a  weak  race." 

Von  Noorden,  however,  is  careful  to  add:  — 

"On  the  other  hand,  the  importance  of  protein  must  not  be 
overestimated.  A  diet  is  not  necessarily  good  because  the  amount 
of  protein  is  right;  it  must  have  the  proper  proportions  of  the 
non-nitrogenous  nutrients  as  well,  since  the  protein  is  not  to  be 
depended  upon  for  the  necessary  fuel  value.  Better  somewhat 
less  protein  with  a  Uberal  amount  of  total  food  than  more  pro- 
tein with  insufficient  fuel  value ;  the  latter  brings  a  rapid  loss  of 
strength,  the  former  can  be  endured  very  well,  at  least  for  a  long 
time,  and  very  hkely  throughout  the  Hfe  of  the  individual." 

Hutchison,  Ln  the  first  edition  of  his  Food  a)id  Dietetics,  took 
similar  ground  regarding  the  desirability  of  Hberal  protein  feed- 
ing and  distinctly  taught  that  large  amounts  of  protein  tend  toward 
a  higher  degree  of  health,  vigor,  and  abihty  to  resist  disease. 

Chittenden,  in  1905,  had  reached  exactly  the  opposite  conclu- 
sion,—  that  the  products  of  protein  metabolism  are  a  constant 
menace  to  the  well-being  of  the  body,  and  that  any  excess  of 
protein  over  what  the  body  actually  needs  is  likely  to  be  directly 
injurious,  and  at  best  puts  an  unnecessary  and  useless  strain  upon 
the  Hver  and  kidneys.  Chittenden  had  satisfied  himself  by  his 
numerous  and  long-continued  experiments  that  both  physical  and 
mental  stamina  are  promoted  by  decreasing  the  amount  of  pro- 
tein in  the  food :  "  Greater  freedom  from  fatigue,  greater  aptitude 
for  work,  greater  freedom  from  minor  ailments,  have  gradually 
become  associated  in  the  writer's  mind  vdih  this  lowered  protein 
metaboUsm  and  general  condition  of  physiological  economy.  .  .  . 
The  ordinary  professional  man  who  leads  an  active  and  even 


FOOD    HABITS    AND   DIETARY    STANDARDS  223 

strenuous  life,  with  its  burden  of  care  and  responsibility,  need  not 
clog  his  system  and  inhibit  his  power  for  work  by  the  ingestion 
of  any  such  quantities  of  protein  food  as  the  ordinary  dietetic 
standards  call  for."  {Physiological  Economy  in  Nutrition,  pp.  51, 
127.) 

Hutchison,  in  the  second  edition  of  his  Food  and  Dietetics, 
does  not  withdraw  his  indorsement  of  the  old  high  protein  stand- 
ard, but  follows  it  with  a  statement  to  the  effect  that  in  view  of 
Chittenden's  work  it  can  no  longer  be  regarded  as  resting  on  an 
entirely  satisfactory  foundation.  More  recently  he  has  concluded 
{Chemical  News,  94,  104,  August  31,  1906)  that  the  normal  amount 
of  protein  in  a  diet  furnishing  3000  calories  should  be  placed  at 
about  75  grams.  This  allows  some  margin  above  the  results  of 
Chittenden's  experiments  and  agrees  with  the  relation  of  protein 
to  calories  in  mother's  milk,  which  Hutchison  regards  as  nature's 
hint  as  to  the  proper  balance  of  nitrogenous  and  non-nitrogenous 
food  for  the  human  species. 

Folin  holds  that  the  argument  for  a  high  protein  diet  based  on 
the  fact  that  large  amounts  of  protein  are  commonly  eaten  by 
those  who  can  afford  it,  can  be  equally  well  applied  to  the  dietetic 
use  of  alcohoUc  beverages  and  is  no  more  convincing  in  one  case 
than  in  the  other;  while  on  the  other  hand,  study  of  protein  me- 
tabolism has  given  rather  strong  evidence  that  the  body  has  no 
need  of  such  amounts  as  are  commonly  eaten ;  for  when  protein 
is  fed  the  nitrogen  which  it  contains  is  usually  eliminated  more 
quickly  than  the  carbon,  and  further  study  indicates  that  a  con- 
siderable part  of  the  nitrogen  absorbed  from  the  alimentary  tract 
never  reaches  the  tissues  at  all,  but  is  converted  into  urea  on  its 
first  passage  through  the  liver. 

The  loss  of  body  nitrogen  which  occurs  in  the  early  periods  of 
restricted  protein  feeding,  and  which  was  not  determined  nor  spe- 
cifically discussed  by  Chittenden,  is  treated  by  Folin  as  follows : 
"All  the  living  protoplasm  in  the  animal  organism  is  suspended  in 
a  fluid  very  rich  in  protein,  and  on  account  of  the  habitual  use  of 


224  CHEMISTRY    OF   FOOD    AND    NUTRITION 

more  nitrogenous  food  than  the  tissues  can  use  as  protein,  the 
organism  is  ordinarily  in  possession  of  approximately  the  maxi- 
mum amount  of  reserve  protein  in  solution  that  it  can  advan- 
tageously retain.  WTien  the  supply  of  food  protein  is  stopped, 
the  excess  of  reserved  protein  inside  the  organism  is  still  sufficient 
to  cause  a  rather  large  destruction  of  protein  during  the  first 
day  or  two  of  protein  starvation,  and  after  that  the  protein  katab- 
olism  is  very  small,  provided  sufficient  non-nitrogenous  food  is 
available.  But  even  then,  and  for  many  days  thereafter,  the 
protoplasm  of  the  tissues  has  still  an  abundant  supply  of  dis- 
solved protein,  and  the  normal  activity  of  such  tissues  as  the 
muscles  is  not  at  all  impaired  or  diminished.  \Vhen  30  grams 
or  40  grams  of  nitrogen  have  been  lost  by  an  average-sized  man 
during  a  week  or  more  of  abstinence  from  nitrogenous  food  [but 
with  an  abundance  of  carbohydrate  and  fat]  the  Hving  muscle 
tissues  are  still  well  supplied  \vith  all  the  protein  that  they  can 
use.  That  this  is  so  is  indicated  on  the  one  hand  by  the  un- 
changed creatinin  elimination,  and  on  the  other  by  the  fact 
that  one  experiences  no  feeling  of  unusual  fatigue  or  of  inabiHty 
to  do  one's  customary  work.  Because  the  organism  at  the  end 
of  such  an  experiment  still  has  an  abundance  of  available  protein 
in  the  nutritive  fluids,  it  is  at  once  seemingly  wasteful  with  nitro- 
gen when  a  return  is  made  to  nitrogenous  food.  This  is  why  it 
only  gradually  and  only  under  prolonged  pressure  of  an  excessive 
supply  of  food  protein  again  acquires  its  original  maximum  store 
of  this  reserve  material.  If  the  interpretation  just  given  for  the 
phenomenon  of  nitrogen  equihbrium  is  correct,  it  constitutes  at 
the  same  time  a  definite  reason  why  the  so-called  standard  diets 
are  unnecessarily  rich  in  protein.  Nitrogen  enough  to  provide 
Uberally  for  the  endogenous  metaboHsm  and  for  the  maintenance 
of  a  sufficient  supply  of  the  reserve  protein  is  shown  to  be  neces- 
sary ;  but  it  ought  neither  to  be  necessary  nor  advantageous  for 
the  organism  to  spUt  ofif  and  remove  large  quantities  of  nitrogen 
which  it  can  neither  use  nor  store  up  as  reserve  material.     In  the 


FOOD    HABITS    AND   DIETARY    STANDARDS  225 

case  of  carnivorous  animals,  the  uncertainty  of  the  food  supply 
has  evidently  led  to  the  development  of  a  capacity  to  store  a 
certain  amount  of  protein  in  the  form  of  increased  muscle  sub- 
stance, but  in  man  this  capacity  seems  not  to  exist.  The  slow- 
ness with  which  the  normal  human  organism  stores  nitrogen  after 
having  lost  only  very  moderate  amounts  does  not  mean  that  the 
human  organism  can  replace  lost  muscle  tissue  only  slowly  and 
with  difhculty.  When  the  organism  really  has  suffered  a  loss 
of  such  tissue,  as  for  example  during  typhoid  fever,  we  know  that 
during  convalescence  there  is  an  astonishingly  rapid  recovery  of 
weight  and  a  correspondingly  extensive  retention  of  nitrogen.  .  .  . 
In  the  light  of  the  theory  developed  in  this  paper  concerning  the 
double  nature  of  protein  metabolism  and  the  explanation  of  the 
phenomenon  of  nitrogen  equihbrium,  the  following  objection  can 
perhaps  be  made  to  the  use  of  large  quantities  of  protein.  The 
excess  of  nitrogen  furnished  with  the  food  is  normally  quickly 
converted  into  urea  and  ehminated,  and  is  therefore  normally 
harmless.  The  continuous  excessive  use  of  protein  may  lead, 
however,  to  an  accumulation  of  a  larger  amount  of  reserve  pro- 
tein than  the  organism  can  with  advantage  retain  in  its  fluid 
media.  It  is  entirely  possible  that  the  continuous  maintenance 
of  such  an  unnecessarily  large  supply  of  unorganized  reserve  ma- 
terial may  sooner  or  later  weaken  one,  or  another,  or  all  of  the 
living  tissues.  At  any  rate,  it  seems  scarcely  conceivable  that 
the  human  organism,  having  all  the  time  access  to  food,  can  gain 
in  efficiency  on  account  of  such  an  excess  of  stored  protein.  The 
carrying  of  excessive  quantities  of  fat  is  considered  as  an  impedi- 
ment, the  carrying  of  excessive  quantities  of  unorganized  protein 
may  be  none  the  less  so  because  more  common  and  less  strikingly 
apparent."  {American  Journal  of  Physiology,  13, 131-132, 136-137.) 
Haliburton,  in  discussing  the  work  of  Chittenden  and  of  Folin, 
concedes  that  "  the  prevalence  of  dyspeptic  troubles  and  uric  acid 
disorders  (among  the  English-speaking  peoples)  should  make  us 
hesitate  before  we  conclude  that  our  diet  has  reached  the  stage 
Q 


226  CHEMISTRY    OF    FOOD   AND   NUTRITION 

of  perfection,  and  should  rather  lead  us  to  admit  that  the  ma- 
jority of  well-to-do  people  eat  too  much  protein,"  but  adds :  "Any 
change  in  the  practice  of  years  and  of  generations  should  be  accom- 
plished gradually,  not  suddenly.  Those  who  are  young  and 
vigorous  may  remember  that  the  hver  is  the  largest  organ  we 
possess,  its  function  is  to  turn  nitrogenous  metabolites  which  may 
be  harmful  into  urea  which  is  harmless  and  easily  disposed  of, 
and  may  gain  comfort  from  the  reflection  that  the  organ  is  ade- 
quate in  health  to  deal  with  large  quantities  of  material.  If  all 
of  us  were  to  reduce  immediately  our  diet  to  the  Chittenden  level, 
we  might  be  hving  perilously  near  the  margin;  any  unusual 
strain,  such  as  privation  or  a  severe  illness,  would  then  find  us 
without  any  reserve  of  nutrient  energy,  and  we  should  probably 
suffer  more  severely  in  consequence. ' '  {A  nnual  Reports  an  Progress 
of  Chemistry,  II,  pp.  215-218.) 

Benedict  argues  that  general  experience  in  animal  feeding 
favors  the  use  of  Uberal  quantities  of  protein,  and  that  "while 
men  may  for  some  months  reduce  the  proportion  of  protein  in 
their  diet  very  markedly  and  apparently  suffer  no  deleterious 
consequences,  yet,  nevertheless,  a  permanent  reduction  of  the 
protein  beyond  that  found  to  be  the  normal  amount  for  man  is 
not  without  possible  danger.  The  fact  that  a  subject  can  so 
adjust  an  artificial  diet  as  to  obtain  nitrogenous  equilibrium  with 
an  excretion  of  nitrogen  amounting  to  about  2  or  3  grams  per 
day  is  no  logical  argument  for  the  permanent  reduction  of  the 
nitrogen  in  food  for  the  period  of  a  lifetime.  .  .  .  Dietary  studies 
all  over  the  world  show  that  in  those  communities  where  produc- 
tive power,  enterprise,  and  civilization  are  at  their  highest,  man 
has  instinctively  and  independently  selected  Hberal  rather  than 
small  quantities  of  protein."  {American  Journal  of  Physiology,  16, 
409.) 

A  similar  position  is  taken  by  Meltzer,  who  compares  the  appe- 
tite for  a  liberal  surplus  of  protein  with  the  Hberal  way  in  which 
the  body  is  proWded  with  organs  and  tissues  for  nearly  all  of  its 


FOOD    HABITS    AND    DIETARY    STANDARDS  227 

functions,  and  concludes  that  "valuable  as  the  facts  which  Chit- 
tenden and  his  co-laborer  found  may  be,  they  do  not  make  obvious 
their  theory  that  the  minimum  supply  is  the  optimum  —  the 
ideal.  The  bodily  health  and  vigor  which  people  with  one  kid- 
ney still  enjoy  does  not  make  the  possession  of  only  one  kidney 
an  ideal  condition.  The  finding  that  the  accepted  standard  of 
protein  diet  can  be  reduced  to  one  half  can  be  compared  with  the 
finding  that  the  inspired  oxygen  can  be  reduced  to  one  half  with- 
out affecting  the  health  and  comfort  of  the  individual,  but  no 
one  deduces  from  the  latter  fact  that  the  breathing  of  air  so  rarefied 
would  be  the  ideal.  .  .  .  The  storing  away  of  protein,  like  the 
storing  away  of  glyqogen  and  fat,  for  use  in  expected  and  unex- 
pected exceptional  conditions  is  exactly  like  the  superabundance 
of  tissues  in  an  organ  of  an  animal,  or  hke  an  extra  beam  in  the 
support  of  a  building  or  a  bridge  —  a  factor  of  safety.  I  there- 
fore believe  that  with  regard  to  the  function  of  supply  of  tissues 
and  energy  by  means  of  protein  food  nature  meant  it  should  be 
governed  by  the  same  principle  of  affluence  which  governs  the 
entire  construction  of  the  animal  for  the  safety  of  its  life  and  the 
perpetuation  of  its  species."     {Science,  25,  481.) 

In  view  of  the  arguments  of  Benedict  and  of  Meltzer,  it  is  of 
especial  interest  that  in  his  later  book  Chittenden  says:  "It  is 
certainly  just  as  plausible  to  assume  that  increase  in  the  con- 
sumption of  protein  food  follows  in  the  footsteps  of  commercial 
and  other  forms  of  prosperity,  as  to  argue  that  prosperity  or 
mental  and  physical  development  are  the  result  of  an  increased 
intake  of  protein  food.  Protein  foods  are  usually  costly  and  the 
ability  of  a  community  to  indulge  freely  in  this  form  of  dietetic 
luxury  depends  in  large  measure  upon  its  commercial  prosperity." 
Moreover,  Chittenden  contends  that  his  allowance  of  60  grams 
of  protein  per  day  for  a  man  of  average  size  is  a  perfectly  trust- 
worthy figure,  with  a  reasonable  margin  of  safety;  that  "dietetic 
requirements,  and  standard  dietaries,  are  not  to  be  founded  upon 
the  so-called  cravings  of  appetite,  but  upon  reason  and  intelligence 


228  CHEMISTRY    OF    FOOD   AXD    NUTRITION 

reenforced  by  definite  knowledge  of  the  real  necessities  of  the 
bodily  machinery";  that  "we  must  be  ever  mindful  of  the  fact, 
so  many  times  expressed,  that  protein  does  not  undergo  com- 
plete oxidation  in  the  body  to  simple  gaseous  products  like  the 
non-nitrogenous  foods,  but  that  there  is  left  behind  a  residue  not 
so  easily  disposed  of";  and  that  "there  are  many  suggestions  of 
improvement  in  bodily  health,  of  greater  efficiency  in  working 
power,  and  of  greater  freedom  from  disease,  in  a  system  of  die- 
tetics which  aims  to  meet  the  physiological  needs  of  the  body 
without  imdue  waste  of  energy  and  unnecessary  drain  upon  the 
functions  of  digestion,  absorption,  excretion,  and  metaboUsm  in 
general.  .  .  ."     {Tlie  Nutrition  of  Man,  pp.  i6o,  164,  227,  269.) 

Plainly  the  dietary  habit  of  well-to-do  people  and  the  die- 
tary standards  which  have  been  generally  accepted  in  the  past 
tend  to  be  decidedly  liberal  with  respect  to  protein,  and  to 
prescribe  it  in  quantities  which  may  be  believed  to  be  benefi- 
cial but  certainly  are  not  knowTi  to  be  necessary.  It  does  not 
seem  advisable,  however,  to  adopt  as  a  standard  the  lowest 
amount  of  protein  to  which  the  body  can  adjust  itself,  but 
rather  to  regard  as  the  normal  requirement  an  amount  w^hich 
will  enable  the  body  to  maintain  not  only  its  equilibrium, 
but  also  some  such  reserve  store  of  protein  as  we  are  accus- 
tomed to  carry.  Where  a  low  protein  diet  is  desired  either 
for  physiological  or  economical  reasons,  we  would  suggest 
an  allowance  of  about  75  grams  of  protein  per  man  per 
day,  and  for  an  average  diet  about  icx)  grams  per  man  per 
day. 

A  reasonable  surplus  of  protein,  from  suitable  food  materials, 
can  hardly  be  injurious  and  may  be  advantageous.     Whether 


# 


FOOD    HABITS   AND   DIETARY   STANDARDS  229 

such  a  surplus  should  be  especially  recommended  or  not  is 
largely  an  economic  question.  Where  little  can  be  spent  for 
food  and  there  is  danger  that  too  little  food  may  be  eaten, 
it  would  be  a  mistake  to  use  a  surplus  of  protein  which  could 
economically  be  replaced  by  other  food  of  greater  fuel  value. 
In  such  cases  one  must  not  be  misled  by  the  popular  state- 
ment that  "protein  builds  tissue"  into  supposing  that  a  lib- 
eral amount  of  protein  can  keep  the  body  strong  in  spite  of  a 
deficiency  in  the  total  food.  This  impression  is  still  somewhat 
general,  but  is  certainly  incorrect. 

The  body  is  weakened  through  getting  too  little  food, 
because  body  material  must  then  be  burned  for  fuel.  So  long 
as  the  total  food  be  deficient,  the  loss  of  body  substance  will 
continue,  because  not  only  the  food  protein,  but  body  tissues 
as  well,  must  be  burned  to  meet  the  energy  requirement.  To 
strengthen  the  body  through  the  diet  w^e  must  increase,  not  the 
protein  alone,  but  primarily  the  total  calories. 

Strengthening  or  weakening  of  the  body  by  feeding  ordi- 
narily depends  much  more  upon  the  sufficiency  or  insufficiency 
of  the  total  food  than  upon  the  amount  of  protein  which  it 
contains.  The  nature  of  the  protein  is  also  important  (Chap- 
ter XI),  and  particularly  so  in  the  case  of  the  growing  child 
and  in  pregnancy  and  lactation.  No  less  important  is  it  that 
the  food  shall  furnish,  along  with  the  pirotein,  proper  amounts 
and  proportions  of  the  so-called  ash  constituents  which  are 
considered  in  the  chapters  which  follow. 


230  CHEMISTRY    OF    FOOD    AND    NUTRITION 

REFERENCES 

Atwater,  The  Demands  of  the  Body  for  Nourishment  and  Dietary 
Standards.  Fifteenth  Report  of  the  Storrs  (Conn.)  Agricultural 
Experiment  Station,  pp.  123-146  (1903). 

Benedict.  The  Nutritive  Requirements  of  the  Body.  American 
Journal  of  Physiology,  16,  409  (1906). 

Chittenden.     Physiological  Economy  in  Nutrition  (1905). 

The  Nutrition  of  Man  (1907). 

FoLiN.  A  Theory  of  Protein  Metabolism.  American  Journal  of  Physi- 
ology, 13,  117  (1905)- 

Hutchison.     Food  and  Dietetics. 

Langworthy.  Food  and  Diet  in  the  United  States.  Reprinted  from 
the  Yearbook  of  the  U.  S.  Department  of  Agriculture  for  1907. 

LusK.     Science  of  Nutrition,  Chapter  9,  2d  ed.  (1909). 

Meltzer.  Factors  of  Safety  in  Animal  Structure  and  Animal  Economy. 
Harvey  Society  Lectures,  Vol.  1906-1907,  and  Science,  25,  481  (1907). 

Paton.  On  Folin's  Theory  of  Protein  Metabolism.  Journal  of  Physi- 
ology, 33,  1  (1905)- 

U.  S.  Department  of  Agriculture,  Office  of  Experiment  Stations,  Bulls. 
Nos.  21,  29,  31,  38,  46,  52,  53,  55,  71,  75,  84,  91,  98,  107, 116,  129, 
132,  149,  150,  221,  223  (data  and  discussion  of  dietary  studies). 


CHAPTER    IX 

IRON    IN    FOOD    AND    ITS    FUNCTIONS    IN 
NUTRITION 

So  far  we  have  considered  the  food  requirement  with  refer- 
ence to  proteins,  fats,  and  carbohydrates  only.  In  terms  of 
the  elements,  only  nitrogen,  carbon,  hydrogen,  and  oxygen 
have  been  considered.  That  other  elements  are  essential 
is  of  course  well  known,  and  in  view  of  recent  investigations 
it  is  not  safe  to  assume  that  they  will  be  present  in  sufficient 
quantity  in  any  diet  which  furnishes  the  requisite  amounts  of 
proteins,  fats,  and  carbohydrates.  It  has  become  necessary 
to  consider  the  so-called  ash  constituents  much  more  carefully 
than  has  been  customary  in  the  past. 

In  many  respects  the  compounds  of  iron  may  be  regarded 
as  a  connecting  link  between  the  organic  and  the  inorganic 
foodstuffs  and  body  constituents.  The  human  body  of  60 
to  70  kilograms  is  supposed  to  contain  about  3  grams  of  iron, 
the  greater  part  of  which  exists  as  a  constituent  of  the  hemoglo- 
bin of  the  red  blood  corpuscles,  while  much  of  the  remainder 
is  contained  in  the  chromatin  substance  of  the  cells.  The 
iron  compounds  of  the  body  are  therefore  very  prominent  in 
the  general  metabolism  and  oxidative  processes  of  the  organ- 

231 


232  CHEMISTRY    OF    FOOD   AND    NUTRITION 

ism  as  a  whole,  and  apparently  also  in  the  particular  activities 
of  the  secreting  and  other  specialized  cells. 

It  has  long  been  known  that  iron  is  essential  to  the  nutrition 
of  animals  as  well  as  of  plants,  and  that  small  amounts  of  the 
oxide  or  phosphate  of  iron  occur  in  the  ash  of  all  natural  food 
materials.  A  few  decades  ago  it  was  assumed  that  the  iron 
exists  in  the  food  as  oxide  or  phosphate,  and  that  hemoglobin 
is  formed  in  the  body  by  the  combination  of  protein  with  inor- 
ganic iron.  This  view  was  hardly  consistent  with  the  ideas 
of  animal  metabolism  taught  by  Liebig  and  generally  held  at 
the  time,  but  appeared  to  be  supported  by  the  successful  use 
of  inorganic  iron  in  the  treatment  of  anemia. 

Important  changes  of  view  in  regard  to  the  metabolism  of 
iron  have  followed  so  closely  and  have  depended  so  directly 
upon  the  progress  of  experimental  methods  that  it  seems 
desirable,  in  this  case,  to  review  in  chronological  order  some 
of  the  more  important  steps  in  the  development  of  our  present 
knowledge. 

DEVELOPMENT  OF  MODERN  VIEWS 

The  results  obtained  in  a  number  of  mvestigations  published 
between  1854  and  1884  threw  doubt  upon  the  utilization  of  in- 
organic iron  for  the  production  of  hemoglobin,  since  they  indi- 
cated that  iron  salts  when  injected  act  as  poisons  anc^  are 
quickly  eliminated  from  the  blood,  and  when  given  by  the 
mouth  reappear  almost  quantitatively  in  the  feces,  little,  if 
any,  evidence  of  absorption  being  obtained  except  when  the 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN   NUTRITION      233 

doses  were  so  large  or  long  continued  as  to  cause  irritation  of 
the  intestine. 

In  the  attempt  to  harmonize  this  result  with  clinical  ex- 
perience it  was  suggested  that  the  inorganic  iron  might  act 
by  absorbing  the  hydrogen  sulphide  of  the  intestine,  thus 
protecting  the  food  iron  from  waste. 

The  view  that  medicinal  iron  acts  by  stimulation  of  the 
absorbing  membrane  was  also  advocated  at  about  this 
time.  It  was  held  that  the  amount  of  iron  in  the  ordinary 
food  is  always  sufficient  for  the  needs  of  the  body,  but  that 
sometimes  the  intestinal  mucous  membrane  becomes  so  blood- 
less that  it  cannot  properly  perform  its  functions  of  absorp- 
tion. Under  such  conditions  inorganic  iron  was  believed  to 
stimulate  and  tone  up  the  membrane  so  that  in  a  short  time 
the  increased  absorption  of  food  iron  makes  good  the  defi- 
ciency in  the  blood. 

A  very  suggestive  discussion  of  the  metabolism  of  iron, 
the  effects  of  a  lack  of  iron  in  the  food,  and  the  amounts  of 
iron  required  for  the  maintenance  of  the  body  in  health  was 
pubUshed  by  Von  Hosslin  in  1882,  and  long  before  this  some 
attention  had  been  given  to  the  iron  content  of  food  materials 
by  Boussingault.  Boussingault's  figures,  however,  are  not 
sufficiently  accurate  to  be  of  value  at  the  present  time,  and 
little  attention  was  given  to  the  subject  discussed  by  Von 
Hosslin  until  it  was  reopened  by  Bunge  about  two  years 
later. 

Bunge,  in  1884,  doubting  the  ability  of  the  animal  body  to 


234  CHEMISTRY    OF    FOOD    AND   NUTRITION 

form  hemoglobin  from  inorganic  iron,  undertook  the  study  of 
the  iron  compounds  of  food  materials  in  order  to  find  in  what 
form  iron  is  normally  absorbed  and  from  what  sort  of  iron  com- 
pounds the  growing  organism  ordinarily  forms  its  hemoglobin. 
Practically  all  of  the  iron  of  eggs  was  found  to  be  in  the  yolk. 
Yolk  of  egg  does  not  contain  any  hemoglobin,  but  it  must  con- 
tain substances  from  which  hemoglobin  can  be  formed,  since 
the  incubation  of  the  egg  results  in  the  development  of  hemo- 
globin without  the  introduction  of  anything  from  without. 
Bunge  found  no  inorganic  iron  in  egg  yolk,  but  isolated  con- 
siderable amounts  of  the  precursor  of  hemoglobin,  which  he 
called  ''hematogen,"  and  which  exhibited  the  properties  of  a 
phospho-protein  containing  about  0.3  per  cent  of  iron  in  such 
firm  "organic"  combination  that  it  gives  none  of  the  ordinary 
reactions  of  iron  salts.  In  milk,  cereals,  and  legumes  similar 
organic  compounds  of  iron  and  only  traces  of  inorganic  iron 
were  found.  At  this  time  Bunge  distinctly  stated  that  iron 
occurs  in  food  solely  in  the  form  of  compUcated  organic  com- 
pounds which  have  been  built  up  by  the  life  processes  of  plants. 
In  this  form,  said  Bunge,  is  the  iron  absorbed  and  assimilated, 
and  from  these  compounds  hemoglobin  is  produced. 

In  1890  and  subsequently,  the  absorption  and  assimi- 
lation of  iron  was  studied  by  several  experimenters,  usually 
with  particular  reference  to  the  question  whether  inor- 
ganic or  synthetic  organic  compounds  of  iron  are  absorbed 
and  assimilated,  and  especially  whether  such  preparations 
contribute  directly  to  the  formation  of  hemoglobin.     This 


IRON    IN   FOOD    AND    ITS    FUNCTIONS    IN   NUTRITION       235 

question  is,  of  course,  extremely  important,  not  only  in  con- 
nection with  the  therapeutic  use  of  medicinal  iron,  but  also 
in  its  bearing  upon  the  iron  requirements  in  health :  for  if 
inorganic  iron  could  be  utilized  in  the  body  in  exactly  the 
same  way  as  the  complex  organic  iron  compounds  of  the 
food,  it  would  follow  that  the  iron  of  drinking  water  could 
replace  that  of  food,  and  the  supplying  of  food  iron  would 
be  a  matter  of  indifference  to  a  man  whose  drinking  water 
supplied  a  few  milligrams  of  iron  per  day.  In  opposition 
to  this  view,  Bunge  held  that  little  if  any  inorganic  iron  is 
assimilated  and  that  any  effect  of  medicinal  iron  should  be 
attributed  to  its  action  in  protecting  the  food  iron  from 
loss  in  digestion,  principally  by  absorbing  the  sulphur 
liberated  as  sulphid  through  intestinal  putrefaction. 

Socin  demonstrated  the  superiority  of  the  iron  of  egg 
yolk  over  iron  chloride  by  dividing  a  number  of  mice  into 
groups,  some  of  which  were  fed  on  a  mixture  of  iron-free 
food  and  iron  chloride,  while  others  received  the  same  iron- 
free  food  with  the  addition  of  egg  yolk.  None  of  the  mice 
fed  without  organic  iron  lived  for  more  than  thirty-two 
days,  while  some  of  those  receiving  egg  yolk  lived  as  long 
as  the  experiments  were  continued  (sixty  to  ninety-nine 
days),  and  gained  in  weight. 

Gottlieb,  recognizing  the  fact  that  iron  might  be  absorbed 
and  used  by  the  body,  yet  finally  excreted  with  the  feces, 
determined  the  intestinal  eUmination  of  iron  in  dogs  before 
and  after  subcutaneous  and  intravenous  injections  of  known 


236  CHEMISTRY    OF   FOOD    AND   NUTRITION 

amounts  of  iron  salts.  From  the  results  obtained  it  was 
estimated  that  practically  all  of  the  injected  iron  was  elimi- 
nated by  the  intestines. 

Selensky  fed  dogs  upon  rice  and  observed  the  effect  upon 
the  hemoglobin  content  of  the  blood.  In  one  experiment 
the  percentage  of  hemoglobin  fell  from  18.5  to  13. i  in  nine 
days;  in  another,  from  14.8  to  11.3  in  six  days,  and  on  con- 
tinuing the  diet  the  anemia  became  more  pronounced,  and 
the  dog  died  at  the  end  of  seventeen  days  on  the  rice  diet. 

Voit  studied  the  metabolism  of  iron  in  dogs  by  direct  ob- 
servations of  absorption  and  elimination  in  isolated  sections 
of  the  small  intestine.  Opening  the  peritoneal  cavity,  he 
separated  the  desired  section,  removed  the  contents,  closed 
the  ends,  and  left  the  sac  thus  formed  in  its  normal  position 
after  having  reunited  the  remainder  of  the  intestine.  Under 
these  conditions  the  isolated  section  of  intestine,  while  not 
coming  in  direct  contact  with  anything  taken  by  the  mouth, 
would  still  receive  its  proportional  share  of  anything  elimi- 
nated from  the  body  through  the  intestinal  wall.  By  kill- 
ing and  examining  animals  which  had  been  kept  for  some 
time  after  such  an  operation,  Voit  was  able  to  compare  the 
amount  of  iron  eliminated  through  the  intestinal  wall  with 
the  amounts  contained  in  food  and  feces,  and  thus  to  infer 
the  extent  to  which  the  iron  taken  by  the  mouth  was  ab- 
sorbed and  returned  to  the  intestine  for  eUmination.  In 
fasting,  the  daily  elimination  found  for  each  square  meter 
of  intestinal  surface  was  6  milligrams  in  the  feces  and  the 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN  NUTRITION      237 

same  amount  (per  square  meter  of  surface)  in  the  isolated 
loop  of  intestine.  On  food  poor  in  iron  the  feces  contained 
in  each  of  two  cases  10  milligrams,  the  isolated  loops  6  and 
9  milligrams,  of  iron  per  square  meter  of  intestinal  surface; 
while  on  food  rich  in  iron  the  corresponding  figures  for  two 
experiments  were  43  and  78  milligrams  in  the  feces,  and  8 
and  6  milligrams  in  the  isolated  portion  of  the  intestine. 
Hence  it  appears  that  the  iron  eliminated  in  the  feces  during 
fasting  or  on  food  poor  in  iron  came  from  the  body  through 
the  intestinal  wall,  while  most  of  the  extra  iron  given  with 
the  food  in  the  last  two  experiments  passed  through  the 
alimentary  canal  without  being  absorbed  and  metabolized. 

Stockman,  in  a  paper  upon  the  metabolism  of  iron,  pub- 
lished in  1893,  while  discussing  mainly  the  therapeutics  of 
chlorosis  (a  type  of  anemia  occurring  in  girls  and  young 
women)  undertook  to  solve  the  question  of  the  absorption 
of  inorganic  iron.     He  reasoned  as  follows :  — 

If  inorganic  iron  preparations  given  hj^podermically  will  cure 
chlorosis,  there  can  in  such  cases  be  no  possibility  of  the  iron 
exerting  its  effect  by  the  stimulation  of  the  alimentary  canal 
or  by  combining  wdth  hydrogen  sulphide  in  the  intestine. 

If  iron  sulphide  given  by  the  mouth  cures  chlorosis,  it 
must  be  through  absorption  of  the  iron,  since  ferrous  sulpliide 
has  no  stimulating  effect  and  cannot  take  up  more  sulphur. 

If  bismuth,  manganese,  etc.,  take  up  hydrogen  sulphide 
as  readily  as  iron,  but  are  inert  in  chlorosis,  a  further  indi- 
rect evidence  of  absorption  of  iron  is  obtained. 


238  CHEMISTRY    OF   FOOD    AND    NUTRITION 

Stockman  made  experiments  and  observations  upon  hos- 
pital patients  (of  which  he  cites  nine  cases)  which  appeared 
to  substantiate  each  of  the  three  propositions,  and  thus  to 
establish  the  fact  that  inorganic  iron  preparations  cure 
chlorosis  through  being  absorbed  and  utilized  in  the  for- 
mation of  hemoglobin. 

During  the  years  1894- 189 7  several  investigators  studied 
the  absorption  of  different  forms  of  iron  by  microchemical 
methods.  Suitable  stains  having  been  found  for  the  iden- 
tification of  iron  in  the  microscopic  sections  of  tissue,  it  was 
possible  by  examination  of  the  intestinal  wall  and  the  various 
organs  and  tissues  of  the  body  to  follow  the  absorption, 
storage,  and  elimination  of  the  iron  given  medicinally  or 
occurring  in  the  food.  Macallum  investigated  in  this  man- 
ner the  behavior  of  inorganic  salts  of  iron,  iron  albumi- 
nates, and  the  iron  compound  of  the  egg  yolk,  and  found 
that  iron  taken  in  any  of  these  forms  may  be  absorbed 
from  the  small  intestine. 

Woltering  compared  microchemically  and  by  quantitative 
determination  the  amounts  of  iron  in  the  livers  of  mice, 
rabbits,  and  dogs,  fed  with  and  without  sulphate  of  iron,  and 
reported  an  increase  in  the  iron  content  of  the  liver  and  in 
the  hemoglobin  and  red  corpuscles  of  the  blood  as  the  result 
of  feeding  the  iron  salt. 

Gaule,  using  principally  microchemical  methods,  found 
no  reaction  for  iron  in  the  chyle  under  normal  conditions; 
but  a  distinct  reaction  appeared  in  the  lymph  nodes,  and 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN   NUTRITION      239 

extended  to  the  spleen  soon  after  the  feeding  of  iron  salt 
to  rabbits.  This  absorption  of  inorganic  iron  was  followed 
by  an  increase  in  the  number  of  red  corpuscles  and  percent- 
age of  hemoglobin  in  the  blood. 

In  the  meantime,  Kunkel  and  Egers  studied  especially 
the  influence  of  iron  salts  upon  the  regeneration  of  blood 
after  hemorrhage.  Kunkel  kept  two  dogs  on  a  limited  milk 
diet,  but  gave  one  of  them,  in  addition  to  the  milk,  iron  in 
the  form  of  albuminate.  Each  of  the  animals  was  bled 
every  seven  days,  about  one  third  of  the  total  blood  being 
taken  each  time.  The  iron  in  the  drawn  blood  was  deter- 
mined and  ascertained  to  be  greater  than  the  amount  sup- 
plied by  the  milk,  but  less  than  the  total  iron  received  by 
the  dog  which  was  fed  with  albuminate.  The  experiment 
was  continued  seven  weeks,  at  the  end  of  which  time  the 
blood  and  organs  of  the  dog  which  had  been  kept  on  milk 
alone  were  poorer  in  iron  than  those  of  the  dog  which  had 
received  the  iron  albuminate.  Only  one  animal  was  fed  in 
each  way,  and  no  determinations  of  hemoglobin  are  recorded. 
According  to  Egers,  the  regeneration  of  blood  after  severe 
losses  (one  third  of  the  estimated  total)  is  very  slow  on  food 
poor  in  iron,  unless  medicinal  iron  is  also  given,  when  the 
rate  of  regeneration  becomes  better,  but  not  so  good  as  on 
a  diet  supplying  an  abundance  of  food  iron  alone.  Even 
when  the  diet  was  rich  in  food  iron,  however,  Egers  found 
that  medicinal  iron  appeared  to  aid  the  regeneration  of 
blood  after  hemorrhage. 


240  CHEMISTRY    OF    FOOD    AND    NUTRITION 

These  investigations  having  shown  that  inorganic  iron 
is  at  least  to  some  extent  absorbed  and  carried  to  organs 
which  take  part  in  the  production  of  hemoglobin,  it  became 
of  especial  importance  to  determine  by  long-continued  feed- 
ing experiments  whether  the  inorganic  iron  thus  absorl^ed 
can  take  the  place  of  food  iron  in  the  production  of  hemo- 
globin under  normal  conditions. 

This  question  was  studied  by  Hausermann  in  an  extended 
series  of  experiments  in  Bunge's  laboratory.  The  general 
plan  of  these  experiments  was  to  feed  young  animals  from 
the  end  of  the  normal  suckling  period  upon  food  poor  in  iron, 
usually  milk  and  rice.  One  half  of  the  animals,  however, 
received  ferric  chloride  in  addition  to  this  food.  After  the 
animals  had  been  thus  fed  for  one  to  three  months  and  had 
usually  doubled  in  weight,  they  were  killed,  and  the  amount 
of  hemoglobin  in  the  entire  body  was  estimated;  also,  in 
the  case  of  small  animals,  the  total  amount  of  iron.  Ex- 
periments were  carried  out  in  this  way  upon  24  rats,  17 
rabbits,  and  14  dogs.  The  results  are  summarized  essentially 
as  follows  by  Bunge :  ^  — 

The  rats  all  became  highly  anemic,  for  at  the  end  of  the 
experiment  the  percentage  of  hemoglobin  was  diminished 
to  about  half  that  of  animals  from  the  same  litter  w^hich  had 
received  their  normal  food,  namely,  meat,  flies,  yolk  of  egg, 
fruit,   and   vegetables.     The   rats  which   had   taken   ferric 

1  Physiological  and  Pathological  Chemistry,  Blakiston's  edition,  Phila- 
delphia, 1902,  p.  379. 


IRON   IN   FOOD   AND   ITS   FUNCTIONS    IN   NUTRITION      241 

chloride  in  addition  to  the  milk  and  rice  contained  no  more 
hemoglobin  than  those  which  had  received  milk  and  rice 
only.  Moreover,  the  amount  of  iron  was  in  each  case  the 
same.  In  one  experiment  alone,  in  which  the  addition  of 
ferric  chloride  was  continued  for  three  months,  was  the 
iron  found  to  be  double  as  much  in  the  animals  which  had 
received  it  as  in  those  which  had  only  milk  and  rice.  But 
here  again  the  proportion  of  hemoglobin  remained  the  same 
in  both  instances.  We  thus  see  that  some  iron  is  absorbed 
if  small  doses  of  iron  are  persisted  in  for  a  long  time,  as  well 
as  if  large  amounts  be  suddenly  administered.  But  this 
inorganic  iron,  when  absorbed,  is  not  utilized  in  the  for- 
mation of  hemoglobin  to  any  appreciable  extent,  but  remains 
unused  in  the  tissues.  Whether  inorganic  iron  was  absorbed 
in  the  experiments  which  lasted  only  from  one  to  two  months 
cannot  be  decided ;  it  is  possible  that  some  of  it  was  absorbed 
and  was  again  eliminated  in  the  same  degree.  Certainly  no 
storing  up  nor  increase  of  iron*  could  be  detected  in  the 
whole  organism. 

The  experiments  on  rabbits  gave  less  decisive  results. 
The  average  proportion  of  hemoglobin  in  the  animals  that 
received  inorganic  iron  was  somewhat  higher  than  that  in 
the  animals  which  were  fed  on  milk  and  rice  only.  But  when 
the  great  individual  differences  between  various  animals 
are  taken  into  consideration,  too  much  importance  must 
not  be  ascribed  to  this  slight  divergence.  At  any  rate,  the 
amount  of  hemoglobin  in  the  control  animal,  which  received 


242  CHEMISTRY    OF    FOOD    AND    NUTRITION 

its  normal  diet  —  fresh  green  cabbage,  bran,  etc.  —  was 
nearly  twice  as  high  as  in  the  animal  which  received  the 
inorganic  iron. 

The  experiments  upon  dogs  were  not  attended  with 
decisive  results,  as  dogs  are  not  suitable  animals  for  these 
experiments,  owing  to  the  variation  in  individuals.  More- 
over, the  growth  of  these  animals  after  the  period  of  lactation 
is  at  a  much  slower  rate,  and  their  appetite  is  so  enormous 
that  they  might  readily  be  able  to  assimilate  sufficient  he- 
moglobin even  from  a  material  so  poor  in  iron  as  milk,  while 
their  appetite  remained  normal.  Hausermann  found  the 
largest  proportion  of  hemoglobin  in  a  dog  which  had  been 
fed  exclusively  upon  milk.  The  animals  which  received 
ferric  chloride  in  addition  to  a  milk  diet  certainly  contained 
no  more  hemoglobin  than  animals  from  the  same  litter  which 
were  fed  on  meat  and  bones. 

Abderhalden,  following  Hausermann,  studied  the  subject 
even  more  exhaustively.  In  order  to  ascertain  whether  and 
to  what  extent  sulphides  normally  exist  in  the  alimentary 
canal,  —  a  question  of  special  importance  in  connection  with 
one  view  of  the  mode  of  action  of  inorganic  iron,  —  Abder- 
halden killed  and  examined  rats,  mice,  cats,  dogs,  guinea 
pigs,  and  rabbits  in  the  following  way:  Immediately  upon 
killing  the  animal,  the  abdomen  was  opened  and  the  intestinal 
tract  from  the  esophagus  to  the  rectum  was  ligated  in  sections. 
The  contents  of  each  section  were  then  removed  and  tested 
quaUtatively  for  sulphides.     Hydrogen  sulphide  was  obtained 


IRON   IN   FOOD    AND    ITS    FUNCTIONS    IN    NUTRITION       243 

from  the  contents  of  the  large  intestine  but  not  from  those 
of  the  small  intestine  nor  of  the  stomach.  Hence,  if  in- 
organic iron  acts  by  improving  the  absorption  of  food  iron, 
it  must  do  so  in  some  other  way  than  by  simply  preventing 
its  precipitation  as  sulphide,  since  this  would  not  occur  in  the 
small  intestine,  where  the  principal  absorption  of  iron  takes 
place.  The  next  step  in  the  investigation  was  to  study  by 
microchemical  methods  the  absorption  of  inorganic  iron,  its 
behavior  in  the  body,  and  its  elimination.  Experiments 
were  made  upon  49  rats  from  7  litters,  14  guinea  pigs  from 
6  litters,  12  rabbits  from  2  litters,  10  dogs  from  3  litters, 
and  6  cats  from  2  litters. 

From  all  of  these  experiments,  Abderhalden  concluded 
that  the  complicated  iron  compounds  of  the  normal  food, 
the  iron  in  the  form  of  hemoglobin,  and  hematin,  and  the 
inorganic  iron  were  all  absorbed  in  the  same  general  way, 
stored  in  the  same  organs,  and  eliminated  by  the  same  paths. 

In  studying  the  utilization  by  the  body  of  the  different 
forms  of  iron,  Abderhalden  fed  animals  from  the  end  of  the 
suckling  period,  or,  in  the  case  of  guinea  pigs,  from  birth,  on 
food  poor  in  iron,  and  divided  each  litter  into  two  groups, 
one  of  which  was  given  inorganic  iron  in  addition.  After  a 
sufficient  time  the  animals  were  killed,  and  the  total  hemo- 
globin in  the  body  of  each  was  estimated.  Experiments  of 
this  kind  were  made  upon  48  rats,  44  rabbits,  14  guinea 
pigs,  17  cats,  and  11  dogs.  The  animals  fed  with  food 
poor  in  iron  plus  an  addition  of  inorganic  iron  were  unable 


244  CHEMISTRY    OF    FOOD    AND   NUTRITION 

to  produce  as  much  hemoglobin  as  those  receiving  normal 

food. 

In  these  experiments,  Abderhalden  had  noticed  some  facts 
which  indicated  that  the  favorable  influence  of  inorganic 
iron  upon  metabolism  and  blood  formation  was  greater  on 
a  diet  rich  in  food  iron  than  when  the  amount  of  food  iron 
was  kept  small.  In  order  to  test  this,  experiments  were 
made  with  66  rats,  lo  rabbits,  and  14  guinea  pigs,  in  the 
manner  already  described,  but  with  diets  arranged  to  bring 
out  this  particular  point.  These  experiments  led  to  the 
conclusion  that  the  greater  the  quantity  of  food  iron  pres- 
ent, the  greater  the  influence  of  the  inorganic  iron  upon  the 
hemoglobin  formation. 

Abderhalden's  experiments  also  showed  that  the  pro- 
duction of  hemoglobin  was  not  stimulated  indefinitely  by 
inorganic  iron,  but  only  for  a  short  time,  and  he  concluded 
that,  whfle  inorganic  iron  m.ay  be  absorbed  and  may  favor- 
ably influence  blood  formation,  it  is  not  used  as  material 
for  the  production  of  hemoglobin.  It  has  also  been  found 
clinically  that  medicinal  iron  gives  better  results  w^hen  used 
intermittently  than  when  used  continuously,  which  indicates 
that  the  action  is  due  to  stimulation  rather  than  to  the  in- 
organic iron  actually  going  to  form  hemoglobin. 

Tartakowsky  has  recently  published  a  large  number  of 
microchemical  observations  in  support  of  the  older  view 
that  inorganic  iron  is  used  directly  in  blood  formation,  but 
such  qualitative  experiments  appear  to  be  outweighed  by 


IRON   IN   FOOD   AND    ITS   FUNCTIONS   IN   NUTRITION      245 

the  careful  quantitative  work  of  Hausermann  and  of  Abder- 
halden. 

While  it  cannot  yet  be  stated  positively  that  inorganic  iron 
is  or  is  not  used  by  the  animal  body  as  material  for  the  pro- 
duction of  hemoglobin,  the  best  medical  opinion  appears  to 
support  the  conclusion  reached  by  Abderhalden,  that  hemo- 
globin is  derived  essentially  from  the  organic  iron  compounds 
of  the  food,  while  inorganic  iron  acts  mainly  if  not  entirely  as 
a  stimulus.  This  view  is  strongly  supported  by  Von  Noorden 
in  his  treatise  on  chlorosis  in  Nothnagel's  Encyclopedia  of 
Practical  Medicine^  and  Ehrlich  "and  Lazarus,  writing  on 
anemia  in  the  same  work,  state :  — 

It  is  not  very  probable  that  the  (medicinal)  iron  stored  by  the 
liver  and  spleen  is  directly  employed  in  the  formation  of  hemo- 
globin ;  on  the  contrary,  the  assumption  first  suggested  by  Von 
Noorden  seems  much  more  plausible,  namely,  that  the  iron  exer- 
cises a  direct  irritative  action  on  the  function  of  the  blood-making 
organs. 

THE  IRON  REQUIREMENT  OF  THE  BODY 

A  very  brief  summary  of  the  leading  facts  regarding  the 
normal  nutritive  relations  of  iron  may  well  precede  the  dis- 
cussion of  the  amount  required. 

Iron  is  an  essential  element  of  hemoglobin  and  of  the  chro- 
matin substances,  i.e.  of  the  body  constituents  most  directly 
concerned  with  the  processes  of  oxidation,  secretion,  reproduc- 
tion, and  development.     The  substances  thus  fundamentally 


246  CHEMISTRY    OF   FOOD   AND    NUTRITION 

connected  with  metabolism  processes  contain  their  iron  in 
firm  organic  combination,  as  a  constituent  of  their  charac- 
teristic proteins;  and  the  normal  materials  for  the  production 
of  these  body  constituents  are  the  similar  iron-protein  com- 
pounds of  the  food. 

The  iron  of  the  food  is  absorbed  from  the  small  intestine, 
enters  the  circulation  by  way  of  the  lymph,  and  is  deposited 
mainly  in  the  liver,  spleen,  and  bone  marrow.  Its  final  elimi- 
nation takes  place  mainly  through  the  walls  of  the  intes- 
tines. 

Both  inorganic  and  synthetically  prepared  organic  forms 
of  iron  are  absorbed  from  the  same  part  of  the  digestive 
tract,  stored  in  the  same  organs,  and  eHminated  by  the  same 
paths  as  the  iron  of  the  food.  These  medicinal  forms  of  iron 
often  stimulate  the  production  of  hemoglobin  and  red  blood 
corpuscles. 

Whether  medicinal  iron  actually  serves  as  material  for  the 
construction  of  hemoglobin  is  not  positively  known,  but  we 
have  what  appears  to  be  ample  evidence  that  food  iron  is 
assimilated  and  used  for  growth  and  for  the  regeneration  of 
hemoglobin  to  much  better  advantage  than  are  inorganic  or 
synthetic  forms,  and  that  when  medicinal  iron  increases  the 
production  of  hemoglobin,  its  effect  is  more  beneficial  in  pro- 
portion as  the  food  iron  is  more  abundant  —  a  strong  indica- 
tion that  the  medicinal  iron  acts  by  stimulation  rather  than  as 
material  for  the  construction  of  hemoglobin. 

Evidently,  then,  we  must  look  to  the  food  and  not  to  medi- 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN  NUTRITION      247 

cines  or  mineral  waters  for  the  supply  of  iron  needed  in  normal 
nutrition. 

Comparatively  few  experiments  upon  the  amount  of  food 
iron  required  for  the  maintenance  of  equilibrium  in  man  have 
been  made.  Cetti  and  Breithaupt  ehminated  0.0073  ^.nd 
0.0077  gram  per  day,  respectively,  when  fasting.  Three  men 
observed  by  Stockman  while  receiving  in  the  food  about 
0.006  gram  each  per  day  eliminated  0.0063,  o-oo93)  3,nd 
0.0115  gram,  respectively.  Von  Wendt  found  his  require- 
ments to  range  in  a  number  of  experiments  on  different  diet 
from  0.008  to  0.016  gram  per  day,  the  largest  amount  being 
required  in  a  case  where  the  diet  was  deficient  in  calcium. 
In  three  experiments  by  Sherman  in  which  the  food  contained 
0.0057  to  0.0071  gram  of  iron  there  was  metabolized  0.0055, 
0.0087,  and  0.0126  gram  per  day,  respectively,  and  here  also  the 
amount  of  iron  which  sufficed  for  equilibrium  when  taken  in 
the  form  of  bread  and  milk  (a  diet  rich  in  calcium)  was  in- 
sufficient when  taken  in  the  form  of  a  diet  (poor  in  calcium) 
consisting  of  bread  and  egg  white,  or  bread  alone.  In  this 
case,  however,  the  difference  in  the  economy  of  the  metabo- 
lism of  the  iron  may  have  been  due  not  simply  to  the  change 
in  the  calcium  content  of  the  food,  but  also  to  the  fact  that  the 
digestion  appeared  better  on  the  diet  containing  milk  than  on 
those  without  it. 

Thus  in  the  cases  in  which  the  intake  and  output  of  iron 
have  been  determined,  the  requirement  appears  to  have 
varied  with  individuals  and  with  the  nature  of  the  diet  from 


248  CHEMISTRY    OF    FOOD   AND   NUTRITION 

0.006  to  0.016  gram  (6  to  16  milligrams)  of  iron  per  man  per 
day. 

We  might  conclude  from  these  results  that  a  daily  allow- 
ance of  10  to  12  milligrams  of  food  iron  should  suffice  for  the 
maintenance  of  iron  equilibrium  in  an  average  man  under 
favorable  conditions,  but  until  the  conditions  which  deter- 
mine a  larger  metabolism  of  iron  are  more  clearly  defined,  it 
would  seem  desirable  to  set  a  higher  standard,  perhaps  15 
milligrams  of  food  iron  per  man  per  day. 

In  calculating  the  iron  requirement  for  a  family  dietary,  it 
is  well  to  make  the  allowance  for  women  and  children  more 
liberal  than  would  be  indicated  by  their  total  food  require- 
ment. A  woman  requiring  eight  tenths  as  much  food  as  a 
man  will  probably  require  more  than  eight  tenths  as  much 
iron,  and  a  child  requiring  half  as  much  food  may  easily 
require  more  than  half  as  much  iron;  for  the  influence  of 
menstruation,  pregnancy,  and  lactation  in  women  and  of 
growth  and  development  in  children  may  reasonably  be 
expected  to  affect  the  demand  for  iron  to  an  even  greater  ex- 
tent than  they  affect  the  requirement  for  total  food.  It  is 
probable  that  pregnancy  and  lactation  increase  the  iron 
requirement  of  the  mother  by  at  least  3  miUigrams  per  day, 
and  at  other  times  the  losses  of  blood  in  menstruation  must 
call  for  a  greater  intake  of  iron  than  would  be  needed  by  a 
healthy  man  of  equal  energy  and  protein  requirement. 

Since  milk  is  the  sole  food  of  young  mammals  during  a 
considerable  period  of  rapid  growth,  Bunge  was  surprised  to 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN   NUTRITION      249 

find  only  small  amounts  of  iron  in  milk  ash.  Comparing 
the  composition  of  the  ash  of  milk  with  that  of  the  new-born 
animals  of  the  same  species,  it  was  found  that,  while  other 
constituents  occurred  in  nearly  the  same  relative  proportions, 
the  iron  was  six  times  as  abundant  in  the  ash  of  the  young 
animal  as  in  that  of  the  milk  on  which  it  was  nourished.  That 
the  suckling  animal  grows  rapidly  and  increases  its  blood 
supply  in  spite  of  this  apparent  deficiency  of  iron  in  its  food 
is  due  to  the  fact  that  the  body  contains  a  reserve  supply  of 
iron  at  birth.  In  confirmation  of  this  statement  Bunge  and 
his  pupils  have  published  many  analyses  showing  that  the 
percentage  of  iron  in  the  entire  organism  is  highest  at  birth, 
and  that  during  the  suckling  period  the  amount  of  iron  in  the 
body  remains  about  constant,  notwithstanding  the  increase 
in  body  weight. 

In  all  cases  in  which  the  young  depend  entirely  upon  the 
milk  of  the  mother  during  the  suckling  period  the  body  con- 
stituents of  the  young  must  evidently  be  derived  entirely 
from  the  maternal  organism  either  before  birth  through  the 
placenta  or  after  birth  through  the  milk  glands  of  the  mother 
and  the  digestive  tract  of  the  young.  Since  disordered  diges- 
tion may  readily  lead  to  defective  absorption  of  the  iron  of 
the  food,  nature  apparently  takes  the  precaution  of  conveying 
the  necessary  iron  from  mother  to  offspring  mainly  by  the 
safer  method,  i.e.  through  the  placenta.  Hence  in  the  case  of 
animals  which  feed  solely  upon  milk  for  some  time  after  birth, 
a  relatively  large  amount  of  iron  is  stored  before  birth  for  use 


250  CHEMISTRY    OF   FOOD    AND   NUTRITION 

in  the  formation  of  hemoglobin  during  the  suckling  period. 
This  has  been  shown  by  analysis  to  be  true  of  children,  pup- 
pies, kittens,  and  rabbits.  On  the  other  hand,  guinea  pigs, 
which  feed  on  green  leaves  or  other  food  rich  in  iron  from  the 
first  day  of  Ufe,  are  born  without  this  reserve  store  of  iron 
(Bunge).  From  recent  analyses  it  appears  that  the  percent- 
age of  iron  in  the  human  body  is  about  three  times  as  high 
at  birth  as  at  maturity.  If  it  be  assumed,  as  indicated  by 
Bunge 's  work,  that  during  the  milk  feeding  of  infancy  the 
amount  of  iron  in  the  body  remains  about  constant,  it  would 
follow  that  the  percentage  of  iron  in  the  child's  body  would 
be  reduced  to  that  in  the  adult  when  the  body-weight  becomes 
about  three  times  what  it  was  at  birth,  —  usually  when  a  Uttle 
over  one  year  old,  —  and  that  from  this  time  on  throughout 
the  period  of  growth,  care  should  be  taken  that  the  food  is 
sufficiently  rich  in  iron  to  provide  not  only  for  equiUbrium, 
but  also  for  the  constantly  increasing  blood  supply. 

IRON  IN   FOODS 

Little  weight  can  be  attached  to  such  statements  regarding 
the  iron  content  of  foods  as  are  based  upon  the  data  obtain- 
able from  the  ordinary  tables  of  ash  analyses,  since  these  have 
usually  been  obtained  by  methods  which  are  likely  to  greatly 
overestimate  the  amoimt  of  iron.  In  the  following  table 
are  shown  the  approximate  amounts  of  iron  now  believed  to 
be  present  in  the  average  edible  portion  of  typical  food  ma- 
terials expressed  (i)  in  milUgrams  per  100  grams  of  material 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN  NUTRITION      25 1 

as  purchased,  (2)  in  milligrams  per  100  grams  of  dry  matter, 
(3)  in  milligrams  per  100  grams  of  protein,  (4)  in  milligrams 
per  3000  calories. 

Iron  in  Typical  Food  Materials 


Food 


Beefsteak,  all  lean  .  . 
Beefsteak,  medium  fat  . 

Eggs 

Milk,  whole      .... 
Milk,  skimmed      .     .     . 
Cream  (18.5  per  cent  fat) 
Barley  flour,  patent  .     . 

Corn  meal 

Oatmeal 

Rice,  polished  .... 
Wheat,  flour  .... 
Wheat,  entire  grain  .  . 
Beans,  lima,  dried  .  . 
Beans,  navy,  dried  .  . 
Beans,  string,  fresh    .     . 

Cabbage 

Corn,  sweet      .... 

Peas,  dried 

Potatoes 

Spinach 

Turnips 

Apples 

Prunes,  dried  .... 
Raisins 


Iron  per 
100  Grams 
Fresh  Sub- 
stance, 
Milligrams 


3-85 
2.2 

3-0 

0.24 

0.25 

0.20 

i.o 

I-I5 

3-7 

0.7 

1-5 
5-2 
7.2 
6.7 
1.6 
0.9 
0.8 
5.6 
1.2 
3-8 
0.6 

0-3 
2.9 

3-6 


Iron  per 

100  Grams 

Dry 

Substance, 
Milligrams 


14. 
8 

11.4 
1-7 
2.5 
0.8 
I.I 

1-3 
4.1 
0.8 
1.6 

5-7 
8.0 

7-5 
14.8 
1 1.0 
3-2 
6.2 
5-7 

7-5 
2.0 

3-3 
4.2 


Iron  per 
100  Grams 

Protein, 
Milligrams 


16 

16 

21.S 
7-3 
7-3 
7-3 

12.8 

12.5 

22.4 

10 

14 

37 

40 

30 

70 

56 

26 

23 

55 
135 

49 

78 
136 
137 


Iron  per 

3000 
Calories, 
Milligrams 


97 

47 

57 

10 

20 
5-6 
8.3 
9-5 

26.4 
5-8 

12.8 

42 

60 

55 
112 

84 
23 
46 
42 
350 
47 
15 
28 

30 


252  CHEMISTRY   OF   FOOD   AND   NUTRITION 

Percentages  of  iron  in  some  other  foods  will  be  found  in  the 
tables  of  ash  constituents  in  the  appendix.  Using  these  recent 
data  for  iron  in  food  materials,  approximate  estimates  of  the 
amounts  of  iron  contained  in  20  American  dietaries  have  been 
made.  The  majority  of  these  were  found  to  furnish  12  to  19 
milligrams  of  iron  per  man  per  day.  Apparently  therefore 
the  typical  American  dietary  does  not  contain  any  such  sur- 
plus of  iron  as  would  justify  the  usual  practice  of  leaving  the 
supply  of  this  element  to  chance.  The  available  data  rather 
indicate  that  foods  should  be  selected  with  some  reference  to 
the  kinds  and  amounts  of  iron  compounds  which  they  contain. 

Meats.  —  In  meat  as  ordinarily  eaten  the  iron  exists  largely 
as  hemoglobin,  due  to  the  blood  contained  in  the  muscular 
tissue  as  usually  sold  and  prepared  for  the  table.  Muscular 
tissue  washed  free  from  blood  contains  iron,  but  the  amount 
is  comparatively  small.  Since  fatty  tissue  contains  much  less 
iron,  the  iron  content  of  fat  meat  is  much  lower  than  that  of 
lean,  and  in  order  to  establish  any  useful  estimate  of  the 
amount  of  iron  in  meat  it  is  practically  necessary  to  consider 
the  lean  tissue  alone  or  to  refer  the  iron  to  the  protein  content 
rather  than  to  the  gross  weight  of  the  meat.  When  expressed 
on  the  former  basis,  the  results  will  still  be  influenced  by  the 
extent  to  which  the  blood  has  been  either  accidentally  or  in- 
tentionally removed  from  the  muscle. 

For  fresh  lean  beef  containing  the  full  proportion  of  blood, 
the  results  obtained  by  most  investigators  are  in  satisfactory 
agreement,  and  the  average  figure,  0.00375  per  cent  iron  in 


IRON   IN   FOOD   AND    ITS   FUNCTIONS    IN   NUTRITION      253 

the  fresh  meat  free  from  visible  fat,  can  be  accepted  with 
little  danger  of  serious  error.  This  corresponds  to  about  15 
to  16  milligrams  of  iron  per  100  grams  of  protein  in  beef,  and 
since  no  certain  differences  in  iron  content  in  the  flesh  of  dif- 
ferent species  has  been  shown,  it  is  assumed  for  the  present 
that  approximately  the  same  ratio  of  iron  to  protein  will  hold 
for  meats  in  general. 

The  iron  of  meat,  as  already  mentioned,  is  largely  due  to  the 
blood  retained  in  the  muscular  tissue.  The  nutritive  value 
of  blood  is  often  questioned.  So  far  as  the  iron  compounds 
of  the  blood  are  concerned,  it  seems  to  be  established  that 
hemoglobin  and  hematin  may  be  absorbed  and  assimilated 
to  some  extent,  but  probably  not  to  such  good  advantage 
as  the  iron  compounds  of  eggs,  milk,  and  vegetable  foods. 

Eggs.  —  The  edible  portion  of  hens'  eggs  has  shown  as  the 
average  of  several  analyses  0.0030  per  cent  of  iron.  Whether 
the  iron  content  of  eggs  can  be  increased  by  giving  to  poultry 
food  rich  in  iron,  is  a  disputed  question. 

There  can  be  no  doubt  regarding  the  assimilation  and 
utiUzation  of  the  iron  compounds  of  eggs,  since  they  serve  for 
the  production  of  all  the  iron-holding  substances  of  the  blood 
and  tissues  of  the  chick,  there  being  no  possibility  of  the  in- 
troduction of  iron  from  without  during  incubation. 

Milk.  — Analyses  of  samples  of  cows'  milk  of  various  origin 
have  given  results  varying  from  0.0002  to  0.0003  per  cent,  and 
averaging  0.00024  per  cent  of  iron  in  the  fresh  substance. 
It  cannot  be  doubted  that  the  iron  of  milk  is  readily  ab- 


254  CHEMISTRY    OF    FOOD    AND   NUTRITION 

sorbed  and  assimilated,  since  this  constitutes  the  sole  natural 
source  of  iron  for  all  young  mammals  during  a  period  of  rapid 
growth.  Moreover,  metabolism  experiments  indicate  that 
the  iron  of  milk  is  likely  to  be  utilized  to  especially  good  ad- 
vantage, perhaps  on  account  of  its  association  with  a  high 
proportion  of  calcium. 

The  question  of  the  iron  supply  of  infants  fed  upon  diluted  or 
modified  cow's  milk  may,  however,  be  considered  at  this  point. 
It  is  now  generally  recognized  that  the  best  substitute  for 
mother's  milk  is  obtained  by  diluting  cream  with  a  solution 
of  milk  sugar,  the  product  being  usually  known  as  modified 
milk.  By  varying  the  richness  of  the  cream  and  the  amounts 
of  water  and  milk  sugar  added,  the  composition  of  the  modified 
milk  can  be  controlled  at  will.  In  order  to  ascertain  whether  the 
iron  compounds  in  milk  tend  to  condense  upon  the  fat  glob- 
ules or  for  any  other  reason  are  altered  in  their  distribution 
by  the  rising  of  the  cream,  a  sample  of  mUk  was  allowed  to 
stand,  and  after  the  cream  had  risen,  the  iron  and  nitrogen  con- 
tents were  determined  separately  in  the  upper  half  containing 
all  of  the  cream,  and  in  the  lower  half  which  consisted  of 
skimmed  nulk.  These  analyses  showed  in  the  upper  half 
0.000277  per  cent  of  iron  and  0.54  per  cent  of  nitrogen ;  in  the 
lower  half  0.000293  P^^  ^^^^  o^  i^^^  ^.nd  0.59  per  cent  of  nitro- 
gen. It  is  evident,  therefore,  that  the  ratio  of  iron  to  nitrogen 
was  practically  the  same  in  the  cream  as  in  the  milk.  It  is 
therefore  important  to  recognize  that  the  iron  content  of  cow's 
milk  is  Uttle  if  any  higher  than  that  of  human  milk,  while  the 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN  NUtillTION      255 

protein  content  is  at  least  twice  as  high ;  that  any  modification 
of  cow's  milk  which  reduces  its  protein  content  will  reduce  the 
iron  content  in  practically  the  same  proportion,  and  that  an 
infant  fed  upon  cow's  milk,  modified  or  diluted  to  contain 
less  than  3  per  cent  of  protein,  is  probably  receiving  food 
poorer  in  iron  than  human  milk.  According  to  present 
estimates  an  infant  fed  on  any  modification  of  cow's  milk 
must  consume  the  equivalent  of  nearly  a  quart  of  undiluted 
milk  or  cream  in  order  to  obtain  as  much  iron  as  is  supplied 
daily  in  the  milk  of  the  average  healthy  nursing  mother. 
Since  no  such  quantity  of  cow's  milk  can  safely  be  fed  in  early 
infancy,  it  is  to  be  expected  that  during  the  first  months  of  life 
the  artificially  fed  infant  will  use  up  the  surplus  store  of  iron 
with  which  it  was  born  more  rapidly  than  will  the  child  of  the 
same  age  which  receives  the  milk  of  a  healthy  mother. 

Grain  Products.  —  Iron  in  combination  with  protein  matter 
is  found  in  considerable  quantity  in  the  cereal  grains,  but  the 
greater  part  of  it  is  in  the  germ  and  outer  layers  and  so  is 
rejected  in  the  making  of  the  "finer  "  mill  products,  such  as 
patent  flour,  polished  rice,  and  new-process  corn  meal.  In  view 
of  the  part  which  the  iron  of  the  germ  takes  in  the  sprouting 
of  the  seed  and  the  nutrition  of  the  young  plant,  there  is 
little  room  for  doubt  that  it  is  of  value  also  in  the  animal 
economy.  To  test  the  value  of  the  iron  in  the  outer  layers  of 
the  grain  Bunge  ^  carried  out  the  following  experiment :  — 

A  Utter  of  eight  rats  was  divided  into  two  groups  of  foul 
^  Zeitschrift  fiir  physiologi$che  Chemie,  25,  36  (1898). 


256 


CHfcfMISTRY   OF   FOOD   AND   NUTRITION 


each,  one  group  fed  upon  bread  from  fine  flour,  the  other  upon 
bread  made  from  flour  including  the  bran.  At  the  end  of  the 
fifth,  sixth,  eighth,  and  ninth  weeks,  respectively,  one  rat  of 
each  group  was  killed,  and  the  gain  in  weight,  the  total  amount 
of  hemoglobin,  and  the  percentage  of  hemoglobin  in  the  entire 
body  were  determined.     The  average  results  were  as  follows :  — 

Effect  of  Feeding  Different  Kinds  of  Bread  on  Growth  and  Iron 
Content  of  Body  in  Experiments  with  Rats 


Kind  of  Ration 

Gain  in  Weight  of 
Body 

Total  Hemoglobin 
IN  Body 

Proportion  of 

Hemoglobin  in 

Body 

White  bread     .     . 
Bran  bread .     .     . 

grams 

4.81 

20.76 

grams 
0.2395 
0.3492 

per  cent 

0.613 

0.714 

Here  the  bran-fed  rats  not  only  made  a  much  greater  general 
growtlf,  but  developed  both  a  greater  amount  and  a  higher 
percentage  of  hemoglobin.  There  can  be  no  doubt  that  the 
iron  and  other  ash  constituents  of  the  outer  layers  of  the  wheat 
were  well  utilized  in  these  cases. 

Vegetables  and  Fruits.  —  Not  many  direct  studies  upon  the 
iron  compounds  of  the  fruits  and  vegetables  have  been  made, 
but  Stoklasa  has  separated  from  onions  an  iron-protein  com- 
pound very  similar  to  the  hematogen  obtained  by  Bunge  from 
egg  yolk,  but  containing  a  considerably  higher  proportion  of 
iron.  Preparations  similar  in  properties  were  also  obtained 
from  peas  and  from  mushrooms. 

In  view  of  the  fact  that  the  herbivorous  animals,  which  are 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN   NUTRITION      257 

less  liable  to  anemia  than  the  carnivora,  obtain  their  normal 
food  iron  entirely  from  vegetable  sources  there  is  every  reason 
to  suppose  that  man  makes  good  use  of  the  iron  of  the  fruits 
and  vegetables  in  his  diet.  Moreover,  since  (as  Herter  has 
shown)  anemic  conditions  and  excessive  intestinal  putrefac- 
tion often  go  together,  the  bulkiness  and  laxative  tendency  of 
fruits  and  vegetables,  along  with  their  relatively  high  iron 
content,  is  advantageous  in  combating  the  conditions  which 
give  rise  to  excessive  putrefaction,  and  at  the  same  time  in- 
creasing the  supply  of  food  iron. 

Among  typical  food  materials  omitted  from  the  above 
table  because  of  contauiing  little,  if  any,  iron  may  be  men- 
tioned fat  pork,  bacon,  lard  and  suet,  butter,  salad  oil,  sugars, 
starches,  and  confectionery.  All  of  these  foods  have  high  fuel 
value,  and  many  are  economical  and  highly  important  ele- 
ments in  a  normal  dietary.  Excessive  use  of  these  foods, 
however,  would  tend  to  satisfy  the  appetite  and  supply  the 
body  with  the  needed  fuel  without  furnishing  the  desirable 
amount  of  iron.  On  the  other  hand,  the  fruits  and  fresh  vege- 
tables are  often  regarded  as  of  low  nutritive  value  because  of 
their  high  water  content  and  low  proportions  of  protein  and  fat. 
But  it  is  largely  this  property  which  makes  them  especially 
important  as  sources  of  food  iron,  because  they  can  be  added 
to  the  diet  without  replacing  the  staple  foods  of  high  calorific 
and  protein  value,  and  without  making  the  total  food  consump- 
tion excessive.  Thus  the  above  table  shows  plainly  that  the 
ratio  of  iron  both  to  protein  and  to  fuel  value  is  high  in  nearly 

8 


258  CHEMISTRY    OF   FOOD    AND   NUTRITION 

all  of  the  typical  fruits  and  vegetables,  so  that  in  most  cases 
it  would  be  necessary  to  increase  only  slightly  the  amount  of 
protein  and  fuel  value  derived  from  these  sources,  in  order 
to  effect  a  material  increase  in  the  iron  content  of  the  dietary. 
The  iron  content  of  eggs  is  also  high,  but  the  cost  of  these 
is  often  such  as  to  restrict  their  use  in  families  of  limited 
means,  while  present  methods  of  drying  and  preserving  tend 
to  equalize  the  cost  and  increase  the  available  variety  of  fruits 
and  vegetables  throughout  the  year.  The  ratio  of  iron  to  fuel 
value  is  also  high  in  lean  meat,  but  here,  as  has  already  been 
pointed  out,  the  iron  exists  largely  in  the  form  of  hemoglobin, 
which  appears  to  be  of  distinctly  lower  nutritive  value  than  the 
iron  compounds  of  milk,  eggs,  and  foods  of  vegetable  origin. 
Especially  in  families  where  there  are  young  children  it  would 
be  a  mistake  to  rely  too  largely  upon  meat  as  a  source  of  iron. 
Von  Noorden,  who  is  one  of  the  strongest  advocates  of  a  liberal 
use  of  meat  in  the  adult  dietary,  says  in  regard  to  the  feeding  of 
children :  — 

The  necessity  of  a  generous  supply  of  vegetables  and  fruits 
must  be  particularly  emphasized.  They  are  of  the  greatest  im- 
portance for  the  normal  development  of  the  body  and  of  all  its 
functions.  As  far  as  children  are  concerned,  we  believe  we  could 
do  better  by  following  the  dietary  of  the  most  rigid  vegetarians 
than  by  feeding  the  children  as  though  they  were  carnivora,  oc- 
cording  to  the  bad  custom  which  is  still  quite  prevalent.  .  .  . 
If  we  limit  the  most  important  sources  of  iron,  —  the  vegetables 
and  the  fruits,  —  we  cause  a  certain  sluggishness  of  blood  forma- 
tion and  an  entire  lack  of  reserve  iron,  such  as  is  normally  found 
in  the  Hver,  spleen,  and  bone  marrow  of  healthy,  well-nourished 
individuals. 


IRON   IN   FOOD   AND   ITS   FUNCTIONS   IN   NUTRITION      259 

In  an  experimental  dietary  study  made  in  New  York  City 
it  was  found  that  a  free  use  of  vegetables,  whole  wheat  bread, 
and  the  cheaper  sorts  of  fruits,  with  milk  but  without  meat, 
resulted  in  a  gain  of  30  per  cent  in  the  iron  content  of  the  diet, 
while  the  protein,  fuel  value,  and  cost  remained  practically  the 
same  as  in  the  ordinary  mixed  diet  obtained  under  .the  same 
market  conditions. 

REFERENCES 

Abderhalden.     Physiological  Chemistry,  Chapter  17. 

BuNGE.     Physiological  and  Pathological  Chemistry,  Chapter  25. 

Gaule,  Resorption  von  Eisen  und  Synthese  von  Haemoglobin.  Zeit- 
schrifi  fur  Biologie,  35,  377  (1897). 

Gottlieb.  Ueber  die  Ausscheidungsverhaltnisse  des  Eisens.  Zeit- 
schriftfur  physiologische  Chemie,  15,  371  (1891). 

Maccallum.  On  the  Absorption  of  Iron  in  the  Animal  Body.  Journal 
of  Physiology,  16,  268  (1894) ;  also  Proceedings  Royal  Society  (Lon- 
don), 50,  277  (1891-1892) ;  Quarterly  Journal  of  Microscopical 
Science  (London),  38,  175  (1896). 

NoTHNAGEL.  Encyclopedia  of  Practical  Medicine.  Diseases  of  the 
Blood,  pp.  17,  339  (1905). 

Sherman.  Iron  in  Food  and  its  Functions  in  Nutrition.  Bull.  185, 
Office  of  Experiment  Stations,  U.  S.  Dept.  Agriculture  (1907). 

SociN.  In  welcher  Form  wird  das  Eisen  resorbirt  ?  Zeitschrift  fiir  physio- 
logische Chemie,  15,  93-139  (1891). 

Von  Wendt.  Untersuchungen  ueber  den  Eiweiss  und  Salz-Stoflfwechsel 
beim  Menschen.  Skandinavisches  Archiv  fUr  Physiologic,  17,  211- 
289  (1905). 

Woltering.  Ueber  die  Resorbirbarkeit  der  Eisen-salze.  Zeitschrift  fUr 
physiologische  Chemie,  21,  186  (1895). 


CHAPTER    X 

INORGANIC   FOODSTUFFS   AND   THE   MINERAL 
METABOLISM 

The  eight  chemical  elements,  iron,  calcium,  magnesium, 
potassium,  sodium,  chlorine,  sulphur,  and  phosphorus,  remain 
either  wholly  or  n  part  in  the  ash  of  food  materials  when  the 
latter  are  burned  in  the  air ;  and  when  the  food  is  metabo- 
lized in  the  body,  they  are  (with  perhaps  the  exception  of  iron) 
given  off  chiefly  in  the  form  of  mineral  matter.  These  ele- 
ments and  their  compounds  are  therefore  commonly  referred 
to  as  ash  constituents,  and  their  metabolism  as  mineral  me- 
tabolism. Some  of  these  elements,  however,  enter  the  body  and 
take  part  in  metabolism  as  essential  constituents  of  organic 
material,  and  become  inorganic  only  as  the  organic  matter  is 
oxidized,  while  others  enter  and  leave  the  body  in  the  same 
inorganic  form. 

From  various  estimates  by  different  writers  the  average 
elementary  composition  of  the  human  body  may  be  presumed 
to  be  approximately  as  follows :  — 

Oxygen,  about 65.  per  cent. 

Carbon,  about 18.  per  cent. 

Hydrogen,  about 10.  per  cent. 

260 


INORGANIC   FOODSTUFFS  26 1 

Nitrogen,  about 3.      per  cent. 

Calcium,  about 2.      per  cent. 

Phosphorus,  about i.      per  cent. 

Potassium,  about 0.35  per  cent. 

Sulphur,  about 0.25  per  cent. 

Sodium,  about 0.15  per  cent. 

Chlorine,  about 0.15  per  cent. 

Magnesium,  about 0.05  per  cent. 

Iron,  about 0.004  per  cent. 


Iodine 

Fluorine 

Sihcon 


Very 

minute 

quantities. 


The  so-called  inorganic  elements  exist  in  the  body  and  take 
part  in  its  functions  in  at  least  three  different  ways:  (i)  as 
the  constituents  which  give  rigidity  and  comparative  perma- 
nence to  the  skeleton ;  (2)  as  essential  elements  of  the  proto- 
plasm of  the  active  tissues ;  (3)  as  salts  held  in  solution  in 
the  fluids  of  the  body;  giving  these  fluids  their  characteris- 
tic influence  upon  the  elasticity  and  irritability  of  muscle 
and  nerve,  supplying  the  material  for  the  acidity  or  alkalin- 
ity of  the  digestive  juices  and  other  secretions,  and  yet 
maintaining  the  neutrality  or  slight  alkalescence  of  the 
internal  fluids  as  well  as  their  osmotic  pressure  and  solvent 
power. 

A  man  under  average  conditions  of  diet,  activity,  and  health 
usually  excretes  daily  from  20  to  30  grams  of  mineral  salts, 
consisting  essentially  of  chlorides,  sulphates,  and  phosphates 
of  sodium,  potassium,  magnesium,  and  calcium  (as  well  as 
ammonium  salts  from  the  protein  metabolism). 


262  CHEMISTRY    OF    FOOD    AND   NUTRITION 

METABOLISM   OF   CHLORIDES  —  USE  OF  COMMON 

SALT 

Practically  all  the  chlorine  involved  in  metabolism  enters, 
exists  in,  and  leaves  the  body  in  the  form  of  chlorides ;  much 
the  greater  part  as  sodium  chloride.  The  amount  of  sodium 
chloride  which  is  ordinarily  added  to  food  as  a  condiment  is  so 
large  that  the  amounts  of  sodium  and  chlorine  present  in  the 
various  foods  in  the  fresh  state  become  of  little  practical  con- 
sequence to  dietetics.  Among  animals  the  herbivora  require 
salt  and  the  carnivora  do  not,  the  latter  obtaining  sufficient 
salt  for  their  needs  from  the  flesh,  and  more  especially  from 
the  blood,  of  their  prey. 

Sodium  occurs  (chiefly  as  chloride)  abimdantly  in  the 
blood  and  other  fluids  of  the  animal  body  and  much  less 
abundantly  in  the  tissues.  Potassium,  on  the  other  hand, 
occurs  most  abundantly  in  the  soft  solid  tissues  —  in  the 
corpuscles  of  the  blood,  the  protoplasm  of  the  muscles,  and 
other  organs,  and  also  in  the  highly  specialized  fluids  which 
some  of  the  glandular  organs  secrete,  e.g.  milk  —  and  to  a 
greater  extent  as  phosphate  than  as  chloride.  Since  the  cells 
are  in  constant  contact  with  the  circulating  fluids,  the  abun- 
dance of  potassium  as  phosphate  in  the  cells  and  of  sodium  as 
chloride  in  the  fluids  makes  it  evident  that  the  taking 
up  of  salts  by  the  cells  is  an  active  or  "selective"  process. 
A  conspicuous  function  of  the  salts  in  the  tissues  is 
the  maintenance  of  the  normal  osmotic  pressure,  but  solu- 


INORGANIC  FOODSTUFFS  263 

tions  of  different  salts  of  equal  osmotic  pressure  are  by 
no  means  interchangeable,  and  it  is  not  possible  to  replace 
successfully  the  potassium  in  the  cell  by  an  equivalent  amount 
of  sodium. 

Attention  is  frequently  called  to  the  fact  that  sodium  chlo- 
ride is  the  only  salt  which  man  seems  to  crave  in  greater  quan- 
tities than  occur  naturally  in  his  food,  and  that  he  shares 
this  appetite  with  the  herbivorous  animals.  Bunge  explains 
the  relation  between  vegetable  diet  and  craving  for  salt  some- 
what as  follows:  Most  vegetables  are  rich  in  potassium, 
which  is  ultimately  eliminated  through  the  blood  and  urine 
in  the  form  of  mineral  salts,  largely  as  sulphate.  Potassium 
sulphate  in  the  blood  reacts  to  some  extent  with  sodium 
chloride  forming  potassium  chloride  and  sodium  sulphate,  both 
of  which  are  rapidly  ehminated  by  the  kidneys.  Hence  the 
greater  the  amount  of  potash  in  the  food  the  greater  the  loss 
of  sodium  and  chlorine  from  the  blood  and  the  greater  the 
necessity  for  salt  to  keep  up  the  normal  sodium  chloride 
content  of  the  body.  Bunge  tested  this  theory  upon  his  own 
person  by  taking  18  grams  of  potash  (as  phosphate  and  citrate) 
in  one  day.  This  increased  the  elimination  of  sodium  chloride 
by  6  grams. 

In  his  Physiological  and  Pathological  Chemistry  (Chap- 
ter VII),  Bunge  records  extended  and  interesting  observa- 
tions and  discussion  upon  the  relation  of  diet  to  the  craving 
for  salt,  and  concludes  that  while  one  might  live  without  the 
addition  of  salt  to  the  food  even  on  a  diet  largely  vegetarian, 


264  CHEMISTRY    OF    FOOD    AND   NUTRITION 

yet  without  salt  we  should  have  a  strong  disinclination  to  eat 
much  of  the  vegetables  rich  in  potassium,  such  as  potatoes. 
"The  use  of  salt  enables  us  to  employ  a  greater  variety  of  the 
earth's  products  as  food  than  we  could  do  without  it."  But 
also,  according  to  Bunge ;  "We  are  accustomed  to  take  far  too 
much  salt  with  our  viands.  Salt  is  not  only  an  aliment,  it  is 
also  a  condiment  and  easily  lends  itself,  as  all  such  things  do, 
to  abuse."  While  Bunge's  explanations  may  not  be  entirely 
adequate  in  detail,  there  seems  to  be  little  doubt  as  to  the 
correctness  of  his  main  deductions. 

Sodium  and  chlorine  equilibrium  can  apparently  be  main- 
tained on  less  than  one  fourth  the  amount  of  salt  ordinarily 
eaten.  Since  the  sodium  chloride  taken  with  the  food  passes 
through  the  body  and  is  excreted  by  the  kidneys  without 
undergoing  any  chemical  change,  the  rate  of  excretion  quickly 
adapts  itself  to  the  rate  of  intake  within  wide  variations. 
When  no  salt  is  taken,  the  rate  of  excretion  falls  rapidly  to  a 
point  where  the  daily  loss  is  extremely  slight.  In  a  recent 
experiment  ^  upon  a  salt-free  diet  the  chlorine  excretion  upon 
successive  days  was  as  follows :  — 

I  St  day  4.60  grams  chlorine.  7  th  day  0.46  grams  chlorine. 

2d  day  2.52  grams  chlorine.  8th  day  0.40  grams  chlorine. 

3d  day  1.88  grams  chlorine.  gth  day  0.26  grams  chlorine. 

4th  day  0.87  grams  chlorine.  loth  day  0.22  grams  chlorine. 

5th  day  0.69  grams  chlorine.  nth  day  0.22  grams  chlorine. 

6th  day  0.48  grams  chlorine.  12th  day  0.17  grams  chlorine. 

13  th  day     0.17  grams  chlorine. 

*  Goodall  and  Joslin,  Transactions  of  the  Association  of  American 
Physicians,  23,  92-106  (1908), 


INORGANIC  FOODSTUFFS  265 

Cetti  in  ten  days  of  fasting  excreted  altogether  13.13  grams, 
and  Belli  in  ten  days  on  a  diet  poor  in  salt  lost  11.8  grams  of 
sodium  chloride.  Since  the  body  is  supposed  to  contain  about 
100  grams  of  sodium  chloride,  it  will  be  seen  that  even  when 
there  was  complete  deprivation  of  salt  for  ten  to  thirteen 
days,  the  total  losses  did  not  exceed  10  to  15  per  cent  of 
the  amount'  estimated  as  usually  present  in  the  body. 
The  salt  thus  readily  given  off  by  the  body  has  been  re- 
garded as  a  measure  of  the  excess  which  the  body  has  been 
forced  to  carry  in  consequence  of  the  extravagant  amounts  of 
salt  which  are  commonly  taken  with  the  food.  Magnus-Levy, 
however,  thinks  that  the  reduced  amount  of  sodium  chloride 
left  in  the  body  after  such  a  loss  is  "not  a  physiological  opti- 
mum, but  rather  a  physiological  minimum." 

Moderate  variations  in  the  amount  of  salt  taken  have  no 
significant  effect  upon  the  protein  metabolism ;  large  amounts 
increase  the  quantity  of  protein  katabolized,  and,  through 
overstimulating  the  digestive  tract,  may  also  interfere  with 
the  absorption  and  utilization  of  the  food. 

OCCURRENCE  AND   METABOLISM  OF   SULPHUR 
COMPOUNDS 

Plants  absorb  sulphates  from  the  soil  and  use  the  sulphur 
in  the  synthesis  of  proteins.  Minute  quantities  of  sulphates 
may  be  taken  by  man  in  food  and  drink,  but  much  the  greatest 
part  of  the  sulphur  concerned  in  metabolism  enters  the  body 
in  organic  combination  and,  so  far  as  known,  chiefly  as  pro- 


266 


CHEMISTRY   OF   FOOD   AND   NUTRITION 


tein.  The  metabolism  of  sulphur  is  therefore  a  part  of  the 
protein  metabohsm,  and  in  many  respects  the  metabolism 
of  sulphur  runs  parallel  to  that  of  nitrogen.  In  a  series  of 
ten  experiments  (each  of  3  to  5  days'  duration)  upon  man, 
in  which  the  food  consisted  of  bread  and  milk  in  varying 
amounts  and  proportions,  the  percentage  absorption  from 
the  digestive  tract  was  nearly  the  same  for  the  sulphur  as 
for  the  nitrogen  of  the  food,  and  the  excretion  of  the  end 
products  ran  so  closely  parallel  that  in  every  case  in  which 
the  body  stored  nitrogen  it  also  stored  sulphur,  and  vice  versa. 
It  is  of  course  well  known  that  individual  proteins  show 
relatively  much  greater  differences  in  sulphur  than  in  nitro- 
gen content,  so  that  the  ratio  of  nitrogen  to  sulphur  varies 
widely,  as  is  shown  by  the  following  examples  selected  from 
the  data  for  pure  proteins  compiled  by  Osborne :  — 


Kind  of  Protein 

Nitrogen 

PER   CENT 

Sulphur 

PER  CENT 

Ratio  of  Nitro- 
gen TO  Sulphur 

Legmnin      .     .     . 

18,04 

0.385 

46.9:  I 

Zein    .     . 

. 

16.13 

0.600 

26.9  :  I 

Edestin  . 

. 

18.69 

0.88 

21.2  :  I 

Gliadin   . 

. 

17.66 

1.027 

17.2:  I 

Leucosin 

. 

16.80 

1.280 

13.1  ••  I 

Casein     . 

. 

15.78 

0.80 

19.7:1 

Myosin  . 

. 

16.67 

1.27 

13.1:1 

Serum  globulin     . 

15-85 

I. II 

14.3  :  I 

Egg  albumin    .     . 

15-51 

I.6I6 

9.6 :  I 

Thus,  while  many  proteins  approximate   the   usually   as- 
sumed average  of  16  per  cent  nitrogen  and  i  per  cent  sulphur, 


INORGANIC   FOODSTUFFS 


267 


there  are  considerable  deviations  from  this  ratio  in  both 
directions. 

Under  ordinary  conditions,  however,  no  protein  is  eaten 
in  a  pure  state,  but  only  as  the  material  containing  it  is  used 
as  an  article  of  food.  It  is  therefore  the  proportion  of  sul- 
phur to  the  total  protein  of  the  food  which  determines  the 
ratio  of  sulphur  to  nitrogen  available  for  nutrition. 

The  proportion  of  sulphur  to  total  protein  has  been  deter- 
mined in  a  few  samples  of  representative  foods  with  the 
following  results :  — 


Food  Material 

Sulphur  in  Percentage 
OF  Total  Protein 

Lean  beef 

Eggs 

Milk                                    

0.95-1.00 

1.4 
0.95-1.09 
I.15-1.29 

1.30 

1-55 
0.69-1.00 
0.80-0.94 

1.07 

Wheat  flour,  crackers 

Entire  wheat 

Oatmeal 

Beans 

Peas 

Potatoes 

Taking  these  figures  as  typical,  it  would  appear  that  in 
those  staple  foods  which  contribute  the  greater  part  of  the 
protein  eaten,  the  ratio  of  protein  to  sulphur  does  not  differ 
as  greatly  as  among  the  pure  proteins,  and  that  in  most  cases 
of  ordinary  mixed  diet  there  would  be  consumed  not  far  from 
I  gram  of  sulphur  in  each  100  grams  of  protein.  We  may 
therefore  consider  that  in  health  and  on  an  ordinary  diet 


268  CHEMISTRY    OF   FOOD    AND   NUTRITION 

the  sulphur  requirement  will  be  covered  when  the  protein 
requirement  is  covered. 

When  proteins  (or  their  cleavage  products)  are  oxidized 
in  the  body,  the  sulphur  becomes  converted  for  the  most 
part  into  sulphuric  acid,  which,  of  course,  must  be  neutralized 
as  rapidly  as  it  is  formed,  since  free  sulphuric  acid  even  in 
small  concentration  would  be  very  injurious  to  the  cells. 
The  greater  part  of  the  sulphuric  acid  formed  in  metaboUsm 
appears  in  the  urine  as  inorganic  sulphates ;  a  smaller  part 
is  found  combined  with  organic  radicles  in  the  form  com- 
monly known  as  "ethereal"  or  "conjugated"  sulphates. 
An  ethereal  sulphate  consists  of  a  molecule  of  sulphuric  acid 
in  which  one  hydrogen  is  replaced  by  potassium  (or  possibly 
sodium  or  ammonium)  and  the  other  by  an  aromatic  body, 
ordinarily  an  indoxyl,  skatoxyl,  phenol,  or  cresol,  derived 
from  the  intestinal  putrefaction  of  protein.  The  amount  of 
ethereal  sulphate  or  the  ratio  of  ethereal  to  inorganic  sulphate 
is  quite  variable,  depending  mainly  upon  the  amount  and 
character  of  the  intestinal  putrefaction,  which  in  turn  is  apt 
to  be  considerably  influenced  by  the  food.  On  ordinary 
mixed  diet  about  one  tenth  or  one  twelfth  of  the  sulphate 
sulphur  in  the  urine  ordinarily  appears  as  ethereal  sulphates ; 
but  when  the  meat  in  the  diet  is  replaced  by  milk,  the  putre- 
faction is  usually  lessened  and  the  proportion  of  ethereal 
sulphates  lowered.  In  one  case  of  a  healthy  man  who  had 
been  on  a  bread  and  milk  diet  for  a  week,  only  one  thirtieth 
of  the  sulphate  sulphur  was  in  the  form  of  ethereal  sulphates. 


INORGANIC   FOODSTUFFS  269 

Not  all  of  the  metabolized  sulphur  is  eliminated  as  mineral 
or  ethereal  sulphate;  a  part  is  given  off  in  less  completely 
oxidized  forms.  This  "unoxidized"  or  "neutral"  sulphur 
usually  constitutes  in  healthy  persons  on  full  diet  from  5 
to  15  per  cent  of  the  total  sulphur  eliminated.  In  Folin's 
experiment  upon  very  low  protein  diet,  while  the  total 
sulphur  metabolism  was  markedly  decreased,  the  quantity 
of  neutral  sulphur  excreted  remained  about  constant,  so  that 
the  relative  proportion  of  sulphur  appearing  in  this  form  was 
increased.  In  certain  diseased  conditions  there  may  be 
marked  increase  both  in  the  relative  proportion  and  in  the 
absolute  amount  of  neutral  sulphur. 

OCCURRENCE    AND    METABOLISM    OF    PHOSPHORUS 
COMPOUNDS 

The  phosphorus  compounds  are  as  universally  distributed 
in  the  body  and  as  strictly  essential  to  every  living  cell  as 
are  the  proteins.  Possibly  because  the  crudity  of  the  views 
formerly  held  and  still  sometimes  met  (especially  in  fraudu- 
lent advertisements  of  proprietary  foods)  tended  to  bring 
the  subject  into  ridicule,  the  study  of  the  phosphates  and 
other  phosphorus  compounds  in  food  and  nutrition  was  very 
generally  neglected,  until  quite  recently,  when  the  signifi- 
cance of  phosphorus  in  the  growth,  development  and  func- 
tions of  the  organism  is  at  last  being  adequately  recognized 
and  is  attracting  attention  to  its  nutritive  relations.  Recent 
investigations,  such  as  those  of  Forbes  and  Hart,  make  it 


270  CHEMISTRY    OF   FOOD    AND   NUTRITION 

appear  probable  that  much  of  the  malnutrition  which  has 
been  attributed  to  low  protein  diet  is  really  due  to  a  defi- 
ciency of  phosphorus  (and  possibly  also  of  calcium)  in  the 
food. 

Principal   Groups   of   Phosphorus   Compounds 

Phosphorus  is  taken  in  the  food  and  is  found  in  the  body 
in  at  least  four  classes  of  compounds :  — 

1.  Phosphorized  proteins,  including  the  nucleo-proteins 
of  cell  nuclei,  the  lecitho-proteins,  and  the  true  phospho- 
proteins  such  as  casein  and  ovovitellin. 

2.  Phosphorized  fats  —  lecithins,  lecithans,  kephalins,  etc. 
These  occur  in  large  quantity  in  brain  and  nerve  substances 
and  in  smaller  amounts  in  other  tissues.  Egg  yolk  is  con- 
spicuous among  food  materials  for  its  richness  in  phosphor- 
ized fats,  but  significant  quantities  are  also  found  in  other 
foods. 

3.  Simpler  organic  derivatives  of  phosphoric  acid,  such 
as  the  inosite-phosphoric  acid  ("  phytic  acid "),  whose 
natural  salts,  which  are  collectively  called  '*  phytin  "  or 
"  phytates,"  are  the  most  abundant  phosphorus  compounds 
of  wheat  and  probably  also  of  the  other  grains  and  of  the 
legumes. 

4.  Inorganic  phosphates,  of  which  potassium  phosphate 
is  probably  the  most  abundant  in  the  food  and  in  the  fluids 
and  soft  tissues  of  the  body,  while  calcium  phosphate  is  the 
chief  mineral  constituent  of  the  bones. 


INORGANIC   FOODSTUFFS  27 1 

Phosphates,  P ho spho- proteins  and  Phosphorized  Fats.  — 
Maxwell/  from  observations  upon  germinating  seeds  and 
developing  chick  embryos,  concluded  that  in  each  of  these 
cases  there  was  at  first  a  synthesis  of  phosphorized  fat,  which 
then  took  an  important  part  in  the  construction  of  the  tissues 
of  the  growing  organizm.  Meischer  studied  the  formation 
of  complex  from  simpler  phosphorus  compounds  in  the  adult 
animal  body  by  observations  upon  the  Rhine  salmon,  which 
during  the  breeding  season  remain  a  long  time  in  fresh  water, 
taking  no  food,  but  developing  large  masses  of  roe  and  milt 
at  the  expense  of  muscular  tissue.  This  process  evidently 
involves  the  formation  of  considerable  amounts  of  phos- 
phorized proteins  and  fats  from  simpler  proteins,  fats,  and 
phosphorus  compounds  of  the  muscles.  Paton  ^  has  studied 
the  salmon  of  Scotland  with  similar  results. 

Chiefly  on  account  of  certain  peculiarities  which  had  been 
observed  in  the  artificial  digestion  of  casein,  the  digestibility 
and  nutritive  value  of  the  phosphorized  radicles  of  phospho- 
proteins  was  for  some  time  in  doubt.  In  1897,  however, 
Marcuse,^  working  in  Rohmann's  laboratory,  showed  by 
a  series  of  digestion  and  metabohsm  experiments  with  dogs 
that  about  90  per  cent  of  the  phosphorus  of  the  casein  fed 
was  absorbed  and  utilized. 

Steinitz,^  followed  by  Zadik  ^  and  Leipziger,^  continuing 

*  American  Chemical  Journal,  13,  16  ;  15,  135, 

^Journal  of  Physiology,  22,  333. 

^  Archiv  Physiologic  (PJliiger),  67,  373. 

^  Ibid.,  72,  75.  5  Ibid.,  77,  i.         « Ibid.,  78,  402. 


272  CHEMISTRY    OF    FOOD    AND    NUTRITION 

this  work,  studied,  especially  by  metabolism  experiments  on 
dogs,  the  question  whether  the  phospho-proteins,  when  fed 
to  the  exclusion  of  the  phosphates,  were  able  to  support  a 
storage  of  phosphorus  in  the  body.  Casein  and  ovovitellin 
were  taken  as  typical  phospho-proteins  and  compared  with 
either  myosin  or  edestin  fed  with  inorganic  phosphates. 
Rohmann  ^  summarized  the  results  as  a  whole  and  found 
a  striking  difference  in  the  phosphorus  balances  in  favor  of 
the  phospho-proteins  as  against  the  mixtures  of  simple  pro- 
teins with  inorganic  phosphates.  The  storage  of  nitrogen 
was  also  more  pronounced  in  the  periods  in  which  the  phos- 
phorized  proteins  were  fed.  The  results  appear  to  justify 
Rohmann's  conclusion  that  the  nutritive  functions  of  phos- 
phorized  and  phosphorus-free  proteins  are  not  entirely  the 
same,  the  former  being  especially  adapted  to  furnish  the 
material  for  tissue  growth. 

Moreover,  Ehrstrom  ^  and  Gumpert  ^  have  found,  in  ex- 
periments upon  men,  that  a  smaller  amount  of  phosphorus 
will  maintain  phosphorus  equilibrium  when  taken  in  the  form 
of  casein  than  when  taken  largely  as  dicalcium  phosphate 
or  as  meat  whose  phosphorus  is  largely  in  the  form  of  potas- 
sium phosphate. 

It  does  not  by  any  means  follow,  however,  that  the  simple 
phosphates  are  without  nutritive  value.     Keller  ^  in  a  study 

'^Berlin  klinische  Wochenschrift,  35,  789. 

2  Skandinavisches  Archivfur  Physiologie,  14,  82. 

•  Medische  Klinik,  i,  1037.  ^  Archivfur  Kinder heilkunde,  29,  i. 


M 


INORGANIC   FOODSTUFFS  273 

of  the  phosphorus  metabolism  of  young  children  found  evi- 
dence that  storage  of  phosphorus  was  favored  by  food  (like 
milk)  which  contained  a  Hberal  supply  of  phosphates  in  addi- 
tion to  the  organic  phosphorus  compounds ;  and  Von  Wendt 
found  that  the  loss  of  phosphorus  occurring  on  a  diet  very 
poor  in  ash  could  be  greatly  reduced  by  the  addition  of  di- 
calcium  phosphate  to  the  food.  Moreover,  it  has  recently 
been  shown  independently  by  Forbes  ^  and  by  Hart/  in  ex- 
periments upon  swine,  that  when  a  part  of  the  phosphorus 
requirement  is  covered  by  organic  phosphorus  compounds, 
the  remainder  can  be  given  in  the  form  of  calcium  phosphates 
which  are  then  utiHzed  at  least  for  the  support  of  the  skeleton ; 
and  McCoUum^  beheves  that,  other  things  being  satisfactory, 
all  the  phosphorus  needed  by  an  animal  can  be  drawn  from 
inorganic  phosphates. 

In  cow's  milk  the  greater  part  of  the  phosphorus  appears 
to  exist  as  phosphate,  but  there  can  be  no  doubt  that  the 
milk  phosphorus  as  a  whole  is  available  for  the  needs  of  the 
young  of  the  species,  especially  in  view  of  the  paralleUsm 
pointed  out  by  Bunge  and  Abderhalden  between  the  phos- 
phorus and  calcium  content  of  milk  and  the  rate  of  growth 
of  the  young  of  the  species. 

It  is,  however,  not  without  possible  significance  that  the 
phosphorus  of  human  milk  is  mainly  in  organic  forms 
(Soldner)  and  that,  notwithstanding  its  much  lower  content 

1  See  references  at  end  of  this  chapter. 

2  Research  Bulletin  No.  8,  Wisconsin  Agricultural  Experiment  Station. 


274 


CHEMISTRY    OF   FOOD    AND    NUTRITION 


Species 


Human 
Horse  . 
Cow  . 
Goat  . 
Sheep  . 
Swine  . 
Dog  . 
Rabbit 


No.  OF  Days 

Required  to 

Double  the 

Birth  Weight 


1 80 
60 

47 
22 

IS 

14 

9 

6 


Percentage  Composition  of 
Milk  (Partial) 


Protein      Ash 


1.6 
2.0 
3-5 
3-7 
4.9 

5-2 

7-4 

14.4 


0.2 

0.4 

0.7 

0.78 

0.84 

0.80 

1-33 
2.50 


CaO 


0.03 
0.12 
0.16 
0.20 
0.25 
0.25 

0.45 
o.8q 


P2O5 


0.05 
0.13 
0.20 
0.28 
0.29 
0.31 
0.51 
0.99 


of  total  phosphorus,  human  milk  contains  as  high  a  percentage 
of  lecithin  as  does  cow's  milk  (Stoklasa).  An  infant  fed  on 
diluted  cow's  milk  must  therefore  receive  less  lecithin  and 
presumably  less  of  other  organic  phosphorus  compounds, 
while  it  may  receive  more  total  phosphorus  than  the  breast- 
fed infant.  As  a  source  of  organic  phosphorus  as  well  as 
iron  and  calcium,  egg  yolk  holds  an  important  place  in  the 
dietary  of  the  child,  particularly  when  artificial  feeding  has 
been  practiced  during  the  suckhng  period. 

The  phytates  (phytin)  and  similar  compounds,  whose  oc- 
currence in  food  materials  has  only  recently  been  appreciated, 
are  still  under  active  investigation,  so  that  it  would  be  pre- 
mature to  attempt  to  state  their  exact  nutritive  value  and 
functions  in  metabolism.  It  is  believed  by  some  physiologi- 
cal chemists  that  these  compounds,  although  easily  mistaken 
for  phosphates  in  their  analytical  behavior,  are  of  greater 
nutritive  value.     This  is  doubted  by  some  other  investigators. 


INORGANIC  FOODSTUFFS  275 

In  either  case,  considering  the  quantities  in  which  they  occur 
in  grains  and  other  vegetable  foods,  the  phytates  must  be 
regarded  as  one  of  the  most  important  dietetic  sources  of 
phosphorus.  For  discussion  of  the  results  of  feeding  experi- 
ments with  phosphates  and  phytates,  see  the  recent  publi- 
cations of  Jordan,  Hart,  Forbes,  Cook,  and  their  associates, 
several  of  which  are  included  among  the  references  given  at 
the  end  of  this  chapter. 

It  is  interesting  to  note  that  the  phosphorus  of  wheat 
bran  is  mainly  in  the  form  of  phytates,  which  are  easily  ex- 
tracted and  doubtless  readily  absorbed  from  the  digestive 
tract.  Washed  bran  fed  to  cows  was  found  to  be  constipat- 
ing, indicating  that  the  laxative  property  of  ordinary  bran 
and  whole  wheat  products  is  dependent  not  simply  upon 
mechanical  irritation,  but  largely,  if  not  mainly,  upon  the 
phytates. 

Metabolism  of  Phosphorus  in  Man 

Factors  determining  Phosphorus  Metabolism.  —  The  abun- 
dance of  phosphorized  fat  in  the  brain  and  nerves  led  at  one 
time  to  belief  that  the  extent  of  the  phosphorus  metabolism 
was  mainly  determined  by  mental  and  nervous  work  or 
strain,  but  important  as  are  the  phosphorus  compounds  of 
the  brain  and  nerves,  their  amount  is  too  small  to  per- 
mit the  belief  that  they  are  the  chief  factor  in  the  phos- 
phorus metabolism.  According  to  Voit's  estimate  a  man's 
skeleton  contains  about  1400  grams,  his  muscles  about  130 


276  CHEMISTRY    OF   FOOD    AND   NUTRITION 

grams,  and  his    brain  and  nerves  only  about  12  grams  of 
phosphorus. 

The  phosphorus  of  the  tissues  exists  largely  in  the  form  of 
nucleoproteins,  —  the  characteristic  substances  of  cell  nuclei, 
—  and,  as  these  are  very  active  in  metaboHsm,  there  was  a 
tendency  for  a  number  of  years  to  regard  the  phosphorus 
eHmination  as  largely  a  measure  of  the  metabolism  of  nucleo- 
proteins somewhat  as  the  nitrogen  is  taken  as  a  measure  of 
the  metaboUsm  of  proteins  in  general.  It  is  probable,  how- 
ever, that  such  a  view  of  the  phosphorus  metabolism  is  of 
only  very  Umited  application,  because  of  the  influence  of 
other  factors.  Voit  showed  that  the  material  katabolized 
in  fasting  comes  largely  from  the  bones.  Hence  it  cannot 
be  assumed  that  the  bones  take  no  part  in  the  daily  me- 
tabolism and  while  they  may  undergo  a  less  active  exchange 
of  material  than  the  soft  tissues,  they  possess  such  a  large 
proportion  of  the  phosphorus  in  the  body  that  they 
probably  contribute  a  considerable  part  of  what  is  katabolized 
from  day  to  day.  Moreover,  recent  investigations  indicate 
that  the  soluble  phosphates  of  the  blood  and  lymph  share  with 
the  bicarbonates  and  the  proteins  the  important  functions  of 
maintaining  neutraUty  in  the  body,  and  that  the  neutraU- 
zation  of  acid  by  conversion  of  di-  into  mono-phosphates 
is  followed  by  an  increased  excretion  of  the  acid  phosphate 
in  the  urine.  Finally,  it  is  evident  that  the  amount  of 
phosphorus  metabolized  is  very  directly  influenced  by 
the  amount  taken  in  the  food,   much  of  which  is  in  com- 


INORGANIC   FOODSTUFFS  277 

paratively  simple  forms,  and  if  not  needed  by  the  tissues  is 
probably  converted  into  phosphate  and  eliminated  quite 
rapidly. 

Since  phosphorus  compounds  are  essential  to  all  the  tis- 
sues of  the  body,  the  growth  of  new  tissue  requires  a 
storage  of  phosphorus  along  with  that  of  protein,  but  aside 
from  this  it  is  evident  that  the  phosphorus  metabolism  pre- 
sents a  separate  problem  from  the   metabolism   of  protein. 

Phosphorus  Elimination.  — The  phosphorus  which  has  been 
metabolized  is  excreted  from  the  body  almost  entirely  in 
the  form  of  inorganic  phosphates,  the  organic  phosphorus 
of  the  urine  constituting  as  a  rule  only  i  to  3  per  cent  of  the 
total. ^  Carnivorous  animals  excrete  phosphates  mainly 
through  the  kidneys,  but  in  the  herbivora  the  excretion  occurs 
almost  entirely  through  the  intestinal  wall,  whether  the 
phosphate  be  taken  by  the  mouth,  or  injected  subcutane- 
ously,  or  be  formed  by  katabolism  of  organic  phosphorus 
compounds  in  the  body.  In  man,  the  elimination  of 
metabolized  phosphorus  is  partly  through  the  kidneys  and 
partly  through  the  intestinal  wall,  the  relative  quantities 
in  urine  and  feces  varying  within  rather  wide  limits.  As  a 
rule,  foods  rich  in  calcium,  or  which  yield  an  alkaline  ash, 
tend  to  increase  the  proportion  of  phosphorus  excreted  by 
way  of  the  intestine. 

^  Some  investigators  have  doubted  the  occurrence  of  organic  phos- 
phorus in  urine,  while  others  have  estimated  it  as  high  as  6  per  cent  of  the 
total  urinary  phosphorus. 


278 


CHEMISTRY    OF   FOOD   AND   NUTRITION 


The  Phosphorus  Requirement. — Attempts  have  sometimes 
been  made  to  estimate  the  phosphorus  requirement  from 
the  amount  excreted  in  the  urine.  The  results  thus  ob- 
tained are  too  low,  and  are  largely  responsible  for  the  fact 
that  the  amount  of  phosphorus  required  for  the  normal  nu- 
trition of  man  is  seriously  underestimated  in  many  of  the 
standard  textbooks. 

Since  the  excretion  of  metabolized  phosphorus  through 
the  intestine  is  in  man  too  large  to  be  neglected,  and  too 
variable  to  be  allowed  for  by  calculation,  we  can  expect 
reliable  data  on  phosphorus  requirements  from  those  experi- 
ments only  in  which  the  amounts  of  phosphorus  are  actually 
determined  in  food,  in  feces,  and  in  urine.  In  such  experi- 
ments it  is  found  (as  in  the  case  of  nitrogen)  that  the  out- 
put obtained  upon  the  experimental  days  is  influenced  not 
only  by  the  food  taken  at  the  time,  but  also  by  the  rate  of 
metabolism  to  which  the  body  had  been  accustomed  on  the 
preceding  days.  This  is  shown  by  the  following  results  ob- 
tained in  a  1 2 -day  series  of  experiments  upon  a  healthy  man : — 

Phosphorus  Metabolism  with  Different  Amounts  of  Phosphorus 
IN  THE  Food 


Experimental 
Period 

Phosphorus  per 

Day 

No. 

Duration 

In  food, 
grams 

In  feces, 
grams 

In  urine, 
grams 

Output, 
grams 

Balance, 
grams 

I 

II 

III 

3  days 
6  days 
3  days 

0.40 
0.77 
1-51 

0.45 
0.19 
0.50 

0.70 
0.72 
0.99 

115 
0.91 

1.49 

-0.75 
-  0.14 
+  0.02 

.,J^. 


INORGANIC   FOODSTUFFS  279 

Here  the  output  of  phosphorus  was  greater  in  the  first 
period  with  0.40  gram  in  the  food  than  in  the  second  when 
the  food  furnished  0.77  gram,  probably  because  the  first 
period  followed  and  was  influenced  by  a  preceding  diet 
fairly  rich  in  phosphorus,  whereas  the  output  in  Period 
II  was  influenced  by  the  low-phosphorus  diet  of  Period  I. 
For  the  same  reason  Period  II  offered  favorable  conditions 
for  the  estabhshment  of  equilibrium  on  a  minimum  diet, 
and  the  results  show  that  in  this  case  the  subject  was 
unable  to  reach  equilibrium  on  0.77  gram  per  day,  the 
output  averaging  0.91  gram.  When  the  intake  was  in- 
creased to  1. 5 1  grams,  the  output  rose  rapidly  and  averaged 
1.49  grams.  In  this  case  the  amount  which  would  have 
been  just  sufficient  for  equilibrium  evidently  lay  between 
0.91  and  1.49  grams  per  day. 

Study  of  the  data  from  about  100  phosphorus  balance 
experiments  has  shown  two  instances  in  which  equilibrium 
was  established  upon  as  little  as  0.8  to  0.9  gram  of  phosphorus 
(corresponding  to  about  2  grams  of  P2O5)  per  day,  but  in 
most  cases  1.2  to  1.75  grams  of  phosphorus  (corresponding 
to  2.75  to  4  grams  of  P2O5)  have  been  required  for  equiUb- 
rium.  It  should  be  noted  that  most  of  these  experiments 
were  not  arranged  primarily  to  determine  the  minimum 
phosphorus  requirement,  and  that  the  previous  habit  of 
the  subject  may  in  many  cases  have  led  to  a  rate  of 
excretion  higher  than  the  minimum  which  would  have  suf- 
ficed had  the  experiments  been  conducted  upon  a  plan  sim- 


28o  CHEAnSTRY    OF   FOOD    AND   NUTRITION 

ilar  to  that  followed  by  Chittenden  in  his  study  of  the  pro- 
tein requirement. 

The  data  at  present  available  therefore  indicate  that  it 
may  be  possible  for  man  to  establish  equilibrium  upon 
about  0,9  gram  of  phosphorus  or  2  grams  of  phosphoric 
acid  per  day,  but  that  at  least  1.2  grams  of  phosphorus  or 
2.75  grams  of  phosphoric  acid  per  day  is  usually  needed  to 
maintain  equilibrium  under  ordinary  conditions  with  a  store 
of  phosphorus  such  as  the  body  carries  when  liberally  fed. 

Important  light  has  recently  been  thrown  upon  the 
phosphorus  requirement  by  Hart's  experiments  with  swine. 
One  lot  of  these  animals  was  fed  a  ration  which  sup- 
plied 1. 1 2  grams  phosphorus  (2.56  grams  P2O5)  per  head 
per  day,  almost  entirely  in  organic  form,  while  other  lots 
received  the  same  ration  with  the  addition  of  phosphates 
or  phytates.  It  was  found  that  the  basal  ration  with  its 
smaller  amount  of  phosphorus  was  insufficient  when  the 
animals  reached  about  85  pounds  in  weight,  while  normal 
growth  continued  if  they  had  in  addition  to  this  basal  ration 
a  further  supply  of  phosphorus  either  as  phosphates  or  as 
phytates. 

If  2.5  grams  of  P2O5  is  insufficient  for  a  pig  of  85  pounds,  it 
would  hardly  seem  a  desirable  amount  for  a  growing  child  of 
the  same  size  or  for  a  man  or  woman.  It  is,  however,  im- 
portant to  know  that  with  this  much  phosphorus  in  ordinary 
forms,  the  remainder  could  be  supplied  by  calcium  phosphates 
without  disadvantage. 


inorganic  foodstuffs  28l 

Phosphorus  in  Food  Materials  and  Typical  Dietaries 

A  comparison  of  the  amounts  of  phosphorus  contained 
in  the  food  of  typical  American  families  with  the  amounts 
metabolized  in  the  experiments  above  mentioned  indicates 
that  a  freely  chosen  diet  does  not  always  furnish  an  abun- 
dance of  phosphorus  compounds.  In  20  American  dietaries  of 
families  or  larger  groups  believed  to  be  fairly  representative, 
the  estimated  amount  of  P2O5  furnished  per  man  per  day  was 
below  2.75  grams  in  8  cases,  while  in  only  2  cases  was  there 
less  than  65  grams  of  protein  per  man  per  day  and  in  only  4 
cases  less  than  75  grams  of  protein.  These  results  indicate 
that  present  food  habits  are  more  likely  to  lead  to  a  deficiency 
of  phosphorus  compounds  than  to  a  deficiency  of  protein  in 
the  diet,  and  it  is  not  improbable  that  many  cases  of  mal- 
nutrition are  really  due  to  an  inadequate  supply  of  phosphorus 
compounds. 

Since  the  different  groups  of  phosphorus  compounds  are 
unequally  distributed  in  food  materials,  and  since  they  ap- 
pear to  differ  somewhat  in  nutritive  value,  it  is  altogether 
probable  that  the  choice  of  food  will  influence  to  some  extent 
the  amount  of  food  phosphorus  required.  At  present,  how- 
ever, our  knowledge  of  these  differences  is  not  sufficiently 
exact  as  to  either  the  nutritive  values  of  the  different  forms 
or  the  quantitative  proportions  in  which  they  occur  in  the 
various  foods,  to  justify  numerical  comparison  of  a  wide 
range  of  foods  on  any  other  basis  than  that  of  total  phos- 
phorus content. 


282 


CHEMISTRY    OF   FOOD    AND    NUTRITION 


The  following  table  compares  some  staple  foods  as  sources 
of  phosphorus  in  the  same  way  that  they  are  compared  as 
sources  of  iron  in  the  preceding  chapter. 

Approximate  Amounts  of  P2O5  in  Food  Materials 


Food 


Beef,  all  lean      .     . 

Eggs 

Egg  yolk  .     .     .     . 

Milk 

Wheat,  entire  grain 
Patent  flour  .  .  . 
Low-grade  flour 

Rice,  polished     .     . 

Oatmeal    .     .     .     . 

Beans,  navy,  dried 
Peas,  dried     .     .     . 

Beets 

Carrots  .  .  .  . 
Parsnips  .  .  .  . 
Potatoes  .  .  .  . 
Turnips     .     .     .     . 

Apples       .     .  .  . 

Bananas    .     .  .  . 

Oranges     .     .  .  . 

Pineapples     .  .  . 

Prunes,  dried  .  . 

Almonds  .  .  .  . 
Peanuts  .  .  .  . 
Walnuts    .     .     .     . 


P2O5 

Per  100  Grams 

Edible 

Substance 


grams 
•50 

•37 
i.o 

-215 

.90 
.20 
.37 

.20 
.87 

1. 14 
.91 
.09 
.10 
.19 
.14 
.12 

.03 
•055 
•05 
.06 

.25 

0.87 
0.90 
0.77 


PaOfi 
Per  100  Grams 

P*ROTEIN 


grams 
2.2 

2.7 
6.3 

6.4 

6.4 
2 

2-75 

2.5 

5-2 

5-0 
3-6 
5.6 

9-5 
II. 2 

6.5 
9.2 

7 
4.0 

6.5 
15-6 

7.8 

4.1 

3-5 
4.2 


P2O5 

Per  3000 
Calories 


grams 
12 

7 
8 


75 
1-7 
3-2 

1-5 

6.4 

9-S 
7-4 
5.6 
6.3 
8.7 
4.7 
8.5 

1-3 
1.6 
2.8 
4.2 
2.6 

4.0 
4.8 
3-2 


INORGANIC   FOODSTUFFS  283 

Such  a  comparison  should,  of  course,  be  interpreted  with 
due  regard  to  what  is  known  of  the  character  of  the  phos- 
phorus compounds  in  the  different  t3^es  of  food.  Eggs 
contain  Hberal  amounts  of  phospho-proteins  and  phosphor- 
ized  fats.  Milk  contains  less  of  the  phosphorized  fats,  but  is 
rich  in  phospho-protein  and  also  in  phosphates.  The  phos- 
phorus of  grains  (both  of  the  inner  and  outer  portions)  is 
present  mainly  as  phytates  which  are  readily  available  in 
digestion.  In  meats  and  fish  the  phosphorus  exists  (at  least 
after  cooking)  so  largely  in  the  form  of  simple  phosphates 
that  it  possibly  should  not  be  considered  as  of  equal  value 
with  the  phosphorus  of  other  foods. 

In  general,  therefore,  the  most  practicable  and  economic 
method  of  securing  an  abundance  of  phosphorus  in  suitable 
forms  is  by  the  free  use  of  milk,  eggs,  vegetables,  and  such 
cereal  products  and  breadstuffs  as  contain  at  least  a  part  of 
the  outer  layers  as  well  as  the  inner  portion  of  the  grains. 

SODIUM,  POTASSIUM,   MAGNESIUM,   CALCIUM 

The  distribution  of  sodium  and  potassium  in  the  body 
and  their  mutual  relations  in  metabolism  have  been  referred 
to  in  the  section  on  the  chlorides.  Calcium  and  magnesium 
occur  largely  in  the  skeleton,  but  also  as  essential  elements  of 
the  soft  tissues  and  fluids  of  the  body.  The  functions  of 
calcium  have  been  studied  in  much  greater  detail  than  those 
of  magnesium.  It  is  estimated  that  about  85  per  cent  of  the 
mineral  matter  of  bone,  or  at  least  three  fourths  of  the  entire 


284  CHEMISTRY    OF    FOOD    AND    NUTRITION 

ash  of  the  body,  consists  of  calcium  phosphate.  Over  99 
per  cent  of  the  calcium  in  the  body  belongs  to  the  bones,  the  • 
remainder  existing  partly  in  organic  combination  with  the 
proteins  of  the  various  tissues  and  partly  as  soluble  salts  in  the 
blood  and  other  fluids.  That  calcium  salts  are  necessary  to 
the  coagulation  of  the  blood  has  long  been  known  and  fre- 
quently cited  as  an  example  of  the  great  importance  of  the 
calcium  salts  in  the  animal  economy.  Equally  striking  is 
the  function  of  these  salts  in  respect  to  their  effect  upon  the 
contractility  of  muscular  tissue  as  demonstrated  particularly 
in  the  case  of  heart  muscle. 

It  has  long  been  known  that  heart  muscle  may  be  kept 
beating  normally  for  hours  after  removal  from  the  body  when 
supplied  under  proper  conditions  with  an  artificial  circulation 
of  blood  or  lymph  or  a  water  solution  of  blood  ash.  Howell, 
Loeb,  and  others  have  studied  the  parts  played  by  the  several 
ash  constituents.  The  sodium  salts  take  the  chief  part  in 
the  maintenance  of  normal  osmotic  pressure  and  have  also  a 
specific  influence.  Contractility  and  irritability  disappear 
if  they  are  absent,  but  when  present  alone  they  produce  re- 
laxation of  the  muscle  tissue.  Calcium  salts  are  present  in 
very  much  smaller  quantity,  but  are  also  absolutely  necessary 
to  the  normal  action  of  the  heart  muscle.  When  present  in 
quantities  above  normal,  they  cause  a  condition  of  tonic  con- 
traction ("calcium  rigor")-  There  is  thus  a  sort  of  antago- 
nism between  calcium  on  the  one  hand  and  sodium  (and  potas- 
sium) on  the  other,  and  it  is  found  that  the  alternate  contrac- 


INORGANIC  FOODSTUFFS  285 

tions  and  relaxations  which  constitute  the  normal  beating  of 
the  heart  are  dependent  upon  the  presence  in  the  fluid  which 
bathes  the  heart  muscle  of  calcium  salts  not  only  in  sufficient 
quantity,  but  also  in  the  proper  proportions  to  the  amounts  of 
sodium  (and  potassium)  salts  present.  Other  active  tissues 
of  the  body  doubtless  have  similar  requirements  as  to  the 
presence  of  proper  proportions  of  the  different  inorganic 
salts  in  the  fluids  which  bathe  them. 

Somewhat  as  Howell  and  others  found  an  antagonistic 
action  between  sodium  and  calcium,  so  Meltzer  and  his  as- 
sociates have  found  that  in  some  conditions  there  is  also  a 
distinct  antagonistic  action  between  calcium  and  magnesium. 
They  have  shown,  for  instance,  that  the  injection  of  mag- 
nesium salts  has  a  marked  general  inhibitory  effect  and  that 
this  can  be  quickly  overcome  by  the  subsequent  injection  of 
calcium  salt.  Summarizing  the  results  of  extended  series  of 
investigations  by  himself  and  others,  Meltzer  stated  in  the 
Transactions  of  the  Association  of  American  Physicians  for 
1908 :  — 

"Calcium  is  capable  of  correcting  the  disturbances  of  the  in- 
organic equilibrium  in  the  animal  body,  whatever  the  directions 
of  the  deviations  from  the  normal  may  be.  Any  abnormal  effect 
which  sodium,  potassium,  or  magnesium  may  produce,  whether 
the  abnormality  be  in  the  direction  of  increased  irritability  or  of 
decreased  irritability,  calcium  is  capable  of  reestablishing  the 
normal  equilibrium." 


286  chemistry  of  food  and  nutrition 

Calcium  in  Food  and  Nutrition 

All  of  the  calcium  compounds  of  foods,  as  well  as  of  drink- 
ing waters,  are  capable  of  absorption,  but  not  all  with  the 
same  facility.  Little  systematic  work  has  yet  been  done  on 
the  relative  availabiHty  of  the  ash  constituents  of  the  different 
foods. 

The  amount  of  lime  eliminated  through  the  kidneys  varies 
greatly,  but  probably  does  not  average  much  over  one  tenth 
of  that  taken  in  the  food.  The  fact  that  the  greater  part  of 
the  calcium  in  the  food  reappears  in  the  feces  has  often  been 
interpreted  as  meaning  that  the  requirement  of  the  body  for 
calcium  is  low  and  the  absorption  of  calcium  from  the  food 
is  poor.  It  is  known,  however,  that  the  calcium  of  the  feces 
comes  from  the  body  as  well  as  the  food.  Elimination  from 
the  body  through  the  intestinal  wall  has  been  proved  for 
calcium  as  for  iron. 

Elimination  of  Hme  salts  through  the  intestinal  wall  con- 
tinues in  fasting  and  is  the  principal  way  in  which  lime  is  lost 
from  the  body  whenever  the  food  supplies  insufficient  lime 
for  equilibrium.  In  adults,  lime  may  continue  to  be  lost  for  a 
long  time  without  the  appearance  of  any  distinct  symptoms, 
doubtless  because  in  such  cases  the  bones  are  drawn  upon  to 
make  good  the  losses  from  the  soft  tissues. 

Efed  of  Insufficient  Calcium.  —  Voit  kept  a  pigeon  for  a 
year  on  food  poor  in  calcium  without  observing  any  effects 
attributable  to  the  diet  until  the  bird  was  killed  and  dissected, 


INORGANIC  FOODSTUFFS  287 

when  it  appeared  that,  although  the  bones  concerned  in  loco- 
motion were  still  sound,  there  was  a  marked  wasting  of  lime 
salts  from  other  bones  such  as  the  skull  and  sternum,  which 
in  places  were  even  perforated.  The  injurious  effect  of  an 
insufficient  intake  of  lime  is  of  course  more  noticeable  with 
growing  than  with  full-grown  animals.  Abnormal  weakness 
and  flexibility  of  the  bones  (like  rickets  in  children)  has  been 
produced  experimentally  by  feeding  puppies  with  lean  and 
fat  meat  only,  while  others  of  the  same  litter,  receiving  the 
same  food,  but  with  the  addition  of  bones  to  gnaw,  developed 
normally.  No  animal  is  literally  carnivorous  in  nature,  that 
is,  none  lives  on  flesh  alone;  the  animals  called  carnivora 
always  eat  more  or  less  of  the  bones  of  their  prey. 

According  to  Herter  ^  many  cases  of  arrested  development 
in  infancy  may  be  due  to  an  insufficient  assimilation  of 
calcium  from  the  food.  Such  a  deficiency  in  the  amount 
assimilated  may  be  due  to  defective  digestion  or  to  a  diet 
inadequate  in  calcium  content. 

The  Calcium  Requirement.  —  On  account  of  the  fluctuating 
distribution  of  the  eliminated  calcium  between  urine  and 
feces,  conclusions  regarding  the  calcium  requirement  can  prop- 
erly be  drawn  only  from  those  experiments  upon  calcium 
metabolism  in  which  the  amounts  of  this  element  in  the  food, 
in  the  feces,  and  in  the  urine  have  been  directly  determined. 
Not  many  such  experiments  have  yet  been  made,  and  the 
reported  results  show  considerable  divergence,  the  amounts 

1  On  Infantilism  from  Chronic  Intestinal  Infection,  New  York,  1908. 


288  CHEMISTRY    OF    FOOD    AND    NUTRITION 

required  for  equilibrium  apparently  ranging  from  0.4  to  i.o 
gram  of  calcium  oxide  per  day.  The  extreme  figures  may 
perhaps  be  due  to  exceptional  conditions  or  in  part  to  ana- 
lytical errors.  The  experiments  which  appear  most  reliable 
indicate  a  requirement  of  about  0.7  gram  calcium  oxide  per 
day  as  the  smallest  amount  on  which  to  obtain  equilibrium 
in  a  healthy  man  accustomed  to  ordinary  diet. 

For  much  the  same  reasons  as  in  the  case  of  iron,  liberal 
allowance  should  be  made  in  calculating  family  dietaries. 
The  need  of  an  abundance  of  calcium  for  a  rapidly  growing 
skeleton  is  obvious.  Before  birth,  and  normally  for  several 
months  after,  this  demand  of  the  child  is  satisfied  by  the 
mother,  whose  lime  requirement  is  thus  greatly  increased. 
The  weakening  of  the  bones  and  teeth  which  is  said  to  be  a 
common  accompaniment  of  pregnancy  and  lactation  is  held  by 
Bunge  to  be  largely  due  to  a  preventable  withdrawal  of  lime 
from  these  structures.  After  weaning  and  throughout  the 
early  childhood  there  are  apt  to  be  frequent  disturbances  of 
the  absorption  and  metabolism  of  lime,  in  some  cases  due  to 
distinct  disorders  of  digestion,  in  other  cases  to  more  ob- 
scure irregularities  in  nutrition.  In  order  that  these  fluctua- 
tions shall  not  interfere  with  the  steady  growth  of  the  child, 
it  is  obvious  that  the  food  must  furnish  a  fairly  liberal  surplus 
of  calcium.  Even  under  the  most  favorable  conditions,  a 
rapidly  growing  child  will  obviously  need  more  bone-making 
material  in  proportion  to  its  total  food  than  did  the  men  who 
served  as  subjects  for  the  metabolism  experiments.    Camerer, 


INORGANIC  FOODSTUFFS  289 

in  summarizing  a  long  series  of  investigations  upon  the  food 
requirements  of  children  at  different  ages,  concluded  that  the 
full  amount  of  lime  received  by  the  average  nursling  is  re- 
quired to  maintain  a  normal  rate  of  growth,  and  Bunge,  from 
a  comparison  of  the  calcium  contents  of  different  staple  foods, 
points  out  that  calcium  more  than  any  other  inorganic  ele- 
ment is  likely  to  be  deficient  as  the  result  of  the  change  of  diet 
from  mother's  milk  to  other  forms  of  food. 

If  0.7  gram  is  the  minimum  on  which  an  average  man  can 
maintain  equilibrium,  it  would  seem  that  the  food  of  a  family 
should  furnish  at  least  i  gram  of  calcium  oxide  per  man  per 
day.  This  is  less  than  is  advocated  by  such  recent  writers  as 
Albu  and  Neuberg,  Gautier,  and  Obendoerffer,  yet  the  major- 
ity of  the  American  dietaries  which  have  so  far  been  examined 
in  this  respect  show  less  than  i  gram  of  calcium  oxide  per  man 
per  day,  and  about  one  third  of  them  show  less  than  0.7  gram. 
Since  inorganic  forms  of  calcium  are  utilized  in  nutrition,  the 
lime  of  the  drinking  water  should  be  added  to  that  of  the  food 
in  calculating  the  amount  consumed,  and  to  this  extent  the 
actual  nutritive  supply  is  greater  than  the  dietary  studies 
show,  but  unless  a  very  "hard"  water  be  used  for  drinking,  it 
is  unlikely  that  the  lime  from  this  source  will  cover  more  than 
a  small  part  of  the  calcium  requirement.  Apparently  there 
should  be  more  attention  to  the  choice  of  such  foods  as  will 
increase  the  calcium  content  of  the  dietary. 

The  following  table  shows  the  comparative  richness  in  cal- 
cium of  a  number  of  staple  articles  of  food, 
u 


290  CHEMISTRY    OF   FOOD   AND   NUTRITION 

Approximate  Amounts  of  CaO  in  Food  Materials 


Food 


CaO 
Per  100  Grams 
Edible  Sub- 
stance 


CaO 
Per  100 
Grams  Pro- 
tein 


CaO 

Per  3000 
Calories 


Beef,  all  lean      .    . 

Eggs 

Egg  yolk  .     .     .     . 

Milk 

Wheat,  entire  grain 
Patent  flour  .  .  . 
Low-grade  flour 

Rice,  polished    .    . 

Oatmeal    .     .     .     . 

Beans,  dried  .  . 

Peas,  dried    .  .  . 

Beets 

Carrots     .     .  .  . 

Parsnips    .     .  .  . 

Potatoes    .     .  .  . 

Turnips     .     .  .  . 

Apples       .     .  .  . 

Bananas    .     .  .  . 

Oranges     .     .  .  . 

Pineapples     .  .  . 

Prunes,  dried  .  . 

Almonds  .  .  .  . 
Peanuts  .  .  .  . 
Walnuts    .     .     .     . 


grams 
O.OI 

0.09 
0,2 

0.17 

0.06 

0.025 

0.04 

O.OI 

0.13 

0.22 
0.14 
0.03 
0.08 
0.09 
0.02 
0.09 

0.014 

O.OI 

0.06 
0.02 
0.06 

0.30 

O.IO 
O.ll 


0.045 
0.66 

1-3 
S-i 

0.4 

0.26 

0-3 

0.1 

0.08 

i.o 
0.4 
1.9 
7.6 

5-3 
0.9 
6.9 

3-5 
0.7 
7.8 
5-2 
1.8 

1.4 
0.4 
0.6 


grams 
0.25 

1-7 
1.6 

7.2 

0.52 

0.2 

0.4 

0.08 

o.i 

1.9 
0.9 
1.9 

S.2 
4.1 
0.7 
6.4 

0.6 

0-3 
3-4 

1.4 
0.6 

1.4 
0.5 
0-5 


INORGANIC   FOODSTUFFS  29 1 

It  will  be  seen  that  there  are  enormous  differences  in  the 
calcium  content  of  different  foods.  Milk  is  so  rich  in  calcium 
that  one  need  take  only  400  calories  in  this  form  to  obtain  i 
gram  of  lime,  while  to  get  the  same  amount  of  hme  from  round 
steak  and  white  bread  it  would  be  necessary  to  take  10,000 
calories.  PoHshed  rice  and  new  process  corn  meal  are  even 
poorer  in  lime  than  patent  flour.  The  difference  between  the 
whole  grains  and  the  "fine"  mill  products,  while  not  so  great 
as  in  the  case  of  iron  or  phosphorus,  is  still  considerable.  The 
fruits  and  vegetables  generally  are  fairly  rich  in  calcium, 
and  some  of  the  green  vegetables  are  strikingly  so;  but  in 
most  cases  the  intake  of  calcium  depends  'mainly  upon  the 
extent  to  which  milk  (and  its  products  other  than  butter) 
enters  into  the  dietary.  A  quart  of  milk  contains  rather 
more  calcium  than  a  quart  of  clear  saturated  lime  water, 
and  by  far  the  most  practical  means  of  insuring  an  abun- 
dance of  calcium  in  the  dietary  is  to  use  milk  freely  as  a  food. 

RELATIONS  OF  THE  ASH-CONSTITUENTS  TO  EACH 
OTHER 

From  this  outline  of  the  occurrence  and  functions  of  some 
of  the  individual  ash  constituents,  it  is  evident  that  the  prev- 
alent custom  of  speaking  of  the  ash  of  a  food  as  if  it  were  a 
more  or  less  homogeneous  substance  is  wholly  illogical  and 
incorrect.  Even  elements  so  closely  related  in  chemical 
properties  as  sodium  and  potassium,  or  calcium  and  magne- 
sium, are  not  only  not  interchangeable,  but  in  some  of  their 


292  CHEMISTRY    OF   FOOD    AND    NUTRITION 

functions  are  mutually  antagonistic.  On  the  other  hand, 
calcium  appears  to  exert  a  favorable  influence  upon  the  econ- 
omy of  iron  in  metaboHsm,  inasmuch  as  it  appears  to  be  pos- 
sible to  maintain  equilibrium  upon  a  smaller  amoimt  of  iron 
when  the  food  contains  an  abundance  of  calcium. 

Another  interesting  relation  is  that  of  the  acid-forming  and 
base-forming  elements  of  the  diet.  This  is  illustrated  by 
experiments  upon  so-called  ash-free  diet.  A  diet  of  proteins, 
fats,  and  carbohydrates  which  has  been  freed  from  mineral 
matter  and  leaves  no  ash  on  burning  in  the  air  will  introduce 
no  fixed  bases  into  the  body,  but  will  introduce  sulphuric  acid 
from  the  metabolism  of  the  sulphur  of  the  protein  eaten,  and 
is  therefore  an  "acid-forming"  diet. 

Lunin  fed  mice  with  casein,  fat,  and  cane  sugar,  the  entire 
mixture  being  nearly  free  from  ash.  On  this  food  with  dis- 
tilled water  5  mice  died,  respectively,  after  11,  13, 14,  15,  and 
21  days.  Other  mice  receiving  the  same  food  with  addition  of 
sodium  chloride  only,  lived  no  longer  (6,  10,  11,  15,  17,  and  20 
days).  But  when  the  food  was  given  with  addition  of  sodium 
carbonate  to  neutr^-lize  the  acid  formed  in  katabolism  of  the 
casein,  the  mice  lived  16,  23,  24,  27,  and  30  days,  or  at  least 
50  per  cent  longer  than  in  either  of  the  previous  cases. 

Taylor^  Uved  for  9  days  upon  a  practically  ash-free  diet 
consisting  of  70-75  grams  of  purified  egg  albumen,  120  grams 
of  washed  olive  oil,  and  200  grams  of  sugar,  and  describes  his 

1  University  of  California,  Publications  in  Pathology,  Vol.  I,  No.  7, 
pp.  71-86. 


INORGANIC   FOODSTUFFS  293 

symptoms  as  essentially  those  of  an  acidosis  resulting  from 
lack  of  base-forming  elements  in  the  food. 

Goodall  and  Joslin  ^  have  experimented  with  a  diet  similar 
to  Taylor's,  without  obtaining  similar  evidence  of  acidosis. 
This  would  seem  to  indicate  that  there  are  considerable  differ- 
ences among  individuals  as  regards  susceptibility  to  the  acids 
produced  in  metaboHsm.  In  the  discussion  of  Goodall  and 
Joslin's  results,  Ewing  said :  "Dr.  Taylor  withdrew  the  alka- 
lis and  got  symptoms  which  he  describes  very  clearly.  It 
seems  to  me  that  this  is  just  the  central  point  in  the  whole 
doctrine  of  acid  intoxication  —  how  much  disturbance  of  the 
tissue  alkaHs  can  be  suffered  without  symptoms." 

Wright,^  who  studied  the  epidemic  of  scurvy  among  the 
British  garrison  during  the  siege  of  Ladysmith,  holds  that  the 
occurrence  of  the  disease  followed  a  diminished  alkalinity  of 
the  blood  resulting  from  food  which  furnished  too  htttle  of  the 
bases;  and  Gautier  states  that  foods  which,  like  the  vege- 
tables, have  an  alkaline  ash  act  as  preventives  of  scurvy,  and 
that  the  outbreak  of  scurvy  during  the  siege  of  Paris  was  con- 
nected, not  with  the  use  of  salt  meat,  but  with  the  exhaustion 
of  the  supply  of  vegetables.  The  latter  statement  is  confirmed 
by  several  writers. 

If  susceptibihty  to  scurvy  and  the  injurious  results  of  an  ash- 
free  diet  are  even  partly  due  to  the  disturbance  of  the  balance 

^  Transactions  of  the  Association  of  American  Physicians,  23,  92-106 
(1908). 

2  Cabot's  Diseases  of  Metabolism,  pp.  398-399. 


294  CHEMISTRY    OF   FOOD    AND   NUTRITION 

of  acid-forming  and  base-forming  elements  in  the  food  (and  it 
has  been  suggested  that  such  disturbance  may  also  be  con- 
nected with  other  abnormaUties  of  metaboUsm),  it  would  seem 
to  follow  that  the  normal  dietary  should  be  so  chosen  as  to 
furnish  the  body  enough  base-forming  elements  to  neutralize 
the  mineral  acids  produced  in  metabolism. 

The  balance  of  acid-forming  and  base-forming  elements 
in  foods  may  be  studied  by  determining  chlorine,  sulphur, 
phosphorus,  sodimn,  potassium,  calcium,  and  magnesium, 
calculating  the  equivalent  in  acid  of  the  first  three  elements, 
the  equivalent  in  alkaU  of  the  last  four,  and  finding  the  excess 
of  acid  or  base  as  the  case  may  be  which  would  result  from  the 
complete  oxidation  of  the  food.  While  in  actual  metaboUsm 
the  sulphur  is  not  quite  all  oxidized  to  sulphate  and  the 
ammonia  is  not  quite  all  changed  to  urea,  yet  the  method 
suggested  is  quite  satisfactory  as  a  means  of  comparing  foods 
in  respect  to  their  acid-forming  or  base-forming  tendency  in 
metaboUsm. 

The  tables  on  the  opposite  page  show  the  relative  pre- 
dominance of  acid-forming  or  base-forming  elements  in  some 
t)rpical  food  materials  :  — 

Beef,  free  from  fat,  round  steak,  and  bacon  are  here  taken 
as  representative  of  meats  of  different  degrees  of  fatness. 
So  far  as  known  the  lean  portions  of  aU  other  meats  contain 
about  the  same  excess  of  acid-forming  elements  as  beef. 

It  wiU  be  seen  that  the  grain  products  show  either  a  practi- 
cal balance  or  a  slight  predominance  of  the  acid-forming 


INORGANIC  FOODSTUFFS 


295 


elements.     Milk  shows  a  slight  predominance  of  the  bases. 
Meats  and  eggs  yield  a  considerable  excess  of  acid ;  vegetables 

Foods  in  which  Acid-forming  Elements  Predominate 


Estimated  Excess  Acid-forming 

Elements  Equivalent  to  cc. 

Normal  Acid  per  100  Calories. 


Beef,  free  from  visible  fat    .     .     . 

Eggs 

Round  steak 

Oatmeal 

Wheat  flour 

Wheat,  entire  grain 

Rice . 

Bacon 

Corn,  entire  grain  (high  protein)  . 


10 

9 

6.7 
3-2 
2.7 
2.6 
2.4 

I.O 
O.I 


Foods  in  which  Base-forming  Elements  Predominate 


Celery 

Cabbage    

Potatoes 

Prunes 

Turnips 

Apples 

Milk 

Beans 

Peas 

Com,  entire  grain  (low  protein) 


Estimated  Excess  Base-forming 

Elements  Equivalent  to  cc.  Normal 

Alkali  per  100  Calories 


40 

10-13.6 

9-12 

7.9 
6.6-12.5 

5 

3-3 

2.9H3.8 

1.9 

0.8 


296  CHEMISTRY    OF   FOOD    AND   NUTRITION 

and  fruits  a  considerable  excess  of  bases.^  A  diet  in  which  the 
acid-forming  elements  greatly  predominate  must  result  in  a 
withdrawal  of  fixed  alkalies  from  the  blood  and  tissues  or  an 
increased  circulation  of  ammonia  salts  in  the  body,  neither  of 
which  can  be  regarded  as  advantageous.  While  such  a  diet  is 
more  or  less  habitual  with  carnivora  and  may  not  be  danger- 
ous to  man,  it  must  put  upon  the  body  accustomed  to  mixed 
diet  a  tax  which,  however  small,  might  better  be  avoided, 
especially  as  we  have  no  reason  to  anticipate  any  disadvan- 
tage from  a  predominance  of  base-forming  elements,  which,  if 
not  used  to  neutralize  stronger  acids,  would  take  the  form  of 
bicarbonates  and  thus  aid  in  the  maintenance  of  the  normal 
and  necessary  neutrality  or  faint  alkalescence  of  the  blood 
and  tissues.  It  therefore  seems  desirable  that  in  constructing 
a  dietary  the  foods  in  which  the  acid-forming  elements  pre- 
dominate should  be  so  balanced  by  foods  having  a  predomi- 
nance of  bases  that  the  diet  as  a  whole  may  yield  sufficient 
fixed  bases  to  neutralize  the  mineral  acids  produced  in  its 
metabolism. 

REFERENCES 

Aberhalden.     Physiological  Chemistry,  Chapter  16. 

Albu  and  Neuberg.     Mineralstoffwechsel  (1906). 

BuNGE.    Physiological  and  Pathological  Chemistry,  Chapters  7  and  8. 

*  That  even  the  strongly  acid  fruits  should  yield  an  excess  of  bases  on 
oxidation  depends  on  the  fact  that  the  acidity  of  the  fruit  is  due  to  an 
organic  acid,  usually  not  free,  but  in  the  form  of  an  acid  potassium  salt, 
which  when  burned  leaves  the  potassium  in  the  form  of  carbonate  or 
bicarbonate. 


INORGANIC   FOODSTUFFS  297 

Forbes.  The  Mineral  Elements  in  Animal  Nutrition,  Bull.  201,  Ohio 
Experiment  Station  (1909). 

Specific  Effects  of  Rations  on  the  Development  of  Swine.     Bull. 

213,  Ohio  Experiment  Station  (1910). 

The  Balance  between  Inorganic  Acids  and  Bases  in  Animal  Nutri- 
tion.    Bull.  207,  Ohio  Experiment  Station  (1909). 

Hart,  McCollum,  and  Fuller.  The  R61e  of  Inorganic  Phosphorus  in 
the  Nutrition  of  Animals.  Research  Bull.  No.  i,  Wisconsin  Ex- 
periment Station  (1909). 

Hart,  McCollum,  and  Humphrey.  The  Role  of  the  Ash  Constituents 
of  Wheat  Bran  in  the  Metabolism  of  Herbivora.  Research  Bull. 
No.  5,  Wisconsin  Experiment  Station  (1909). 

Henderson.  Das  Gleichgewicht  zwischen  Basen  und  Saueren  im 
thierischen  Organismus.  Ergehnisse  der  Physiologie,  8,  254-325 
(1909). 

Jordan,  Hart,  and  Patten.  Metabolism  and  Physiological  Effects  of 
Phosphorus  Compounds  of  Wheat  Bran.  Technical  Bull.  No.  i. 
New  York  State  Experiment  Station;  and  American  Journal  of 
Physiology,  16,  268  (1906). 

Osborne.  Sulphur  in  Protein  Bodies.  Journal  of  the  American  Chemi- 
cal Society,  24,  140. 

Sherman,  Mettler,  and  Sinclair.  Calcium,  Magnesium,  and  Phospho- 
rus in  Food  and  Nutrition.  Bull.  227,  Office  of  Experiment  Stations, 
U.  S.  Dept.  of  Agriculture. 

Sherman  and  Sinclair.  The  Balance  of  Acid-forming  and  Base-form- 
ing Elements  in  Food.  Journal  of  Biological  Chemistry,  3,  307 
(1907)- 


CIL\PTER    XI 

CRITERIA  OF  NUTRITIVE  VALUE  AND  ECONOMY 
OF  FOODS 

The  nutritive  value  of  a  food  in  the  sense  in  which  the 
term  is  here  used,  i.e.  the  value  of  the  food  as  a  source  of 
energy  for  maintaining  the  work  of  the  body  and  of  material 
for  preventing  or  replacing  the  waste  of  body  substance  or 
for  g^o^\1:h,  is  chiefly  judged  (i)  by  its  chemical  composi- 
tion, (2)  by  its  behavior  in  digestion,  (3)  by  its  behavior  in 
metabolism. 

CHElVnCAL  COMPOSITION 

In  many  cases  the  nutritive  value  of  a  food  is  assumed  from 
the  results  of  the  chemical  examination  alone,  and  in  routine 
work  such  an  examination  is  commonly  limited  to  a  partial 
proximate  analysis  by  the  conventional  method,  according  to 
which  loss  of  weight  at  100°  C.  is  considered  as  moisture, 
residue  on  burning  to  whiteness  as  ash,  total  nitrogen 
multiplied  by  6.25  as  protein,  material  soluble  in  ether  as 
fat,  and  the  residual  material  (estimated  by  difference)  as 
carbohydrates. 

The  accepted  tables  of  composition  and  fuel  value  of  foods, 
such  as  that  in  Bulletin  28,  Ofl&ce  of  Experiment  Stations, 

298 


VALUE  AND  ECONOMY  OF  FOODS        299 

U.  S.  Department  of  Agriculture,  are  compiled  chiefly  from 
the  results  of  analyses  made  by  this  method. 

In  the  analysis  of  most  of  the  well-known  staple  articles  of 
food  which  ordinarily  furnish  the  greater  part  of  the  nutrients 
in  the  diet,  this  conventional  method  of  proximate  analysis 
yields  sufficiently  serviceable  results.  On  the  other  hand, 
in  the  analysis  of  numerous  special  articles  of  food  or  in  an 
attempt  to  compare  the  food  values  of  very  dissimilar  sub- 
stances, the  results  obtained  by  this  method  may  be  seriously 
misleading.  Nitrogen  may  be  present  in  other  forms  than 
protein,  the  ether  extract  may  contain  other  substances  than 
fat,  and  the  estimation  of  carbohydrates  by  difference  may  in- 
troduce large  errors.  It  is  possible  to  prepare  a  mixture  of 
wet  leather  and  petroleum  jelly  which,  when  subjected  to  the 
usual  routine  analysis,  would  yield  the  same  results  as  meat ; 
and  a  digestion  experiment  with  sheep  has  been  recorded  in 
which  the  dried  samples  of  the  food  and  of  the  feces  yielded 
almost  identical  analytical  data.  Moreover,  it  is  becoming 
more  and  more  apparent  that  even  among  staple  foods  there 
are  many  cases  in  which  the  ordinary  routine  analysis  fails 
to  differentiate  substances  which  are  quite  different  in  nutri- 
tive value.  In  such  cases  it  is  not  safe  to  conclude,  as  is  some- 
times done,  that  there  are  "  differences  which  chemistry  can- 
not show,"  for  chemistry  can  show  vastly  more  than  is  shown 
by  the  partial  analyses  usually  made.  By  the  employment  of 
sufficiently  intricate  and  time-consuming  methods  most  of  the 
individual  organic  substances  which  are  usually  divided  only 


300  CHEMISTRY    OF    FOOD    AND    NUTRITION 

into  the  three  groups  of  proteins,  fats,  and  carbohydrates  can 
be  definitely  differentiated. 

Thus,  while  the  grains  and  many  of  the  vegetables  contain 
most  of  their  carbohydrate  material  in  the  form  of  starch, 
there  are  other  vegetable  foods  in  which  the  chief  form  of  car- 
bohydrate is  inulin,  mannan,  galactan,  or  pentosan.  In  so 
far  as  the  physiological  behavior  of  these  substances  has  been 
determined,  a  chemical  analysis  which  shows  their  presence 
and  amounts  in  a  food  may  guide  us  to  a  correct  estimate  of  its 
nutritive  value,  but  as  yet  the  knowledge  of  chemical  relation- 
ship would  not  in  itself  enable  us  to  predict  the  physiological 
relationships  and  comparative  nutritive  values. 

In  the  case  of  the  proteins,  there  has  recently  been  much 
progress  in  chemical  methods,  both  for  separating  the  proteins 
from  their  natural  mixtures  in  foods,  and  in  determining  the 
constituent  radicles  of  the  individual  proteins.  The  knowledge 
of  the  chemical  structure  of  the  proteins  which  has  thus  been 
gained,  while  not  yet  complete  in  any  instance,  has  already 
explained  differences  in  nutritive  value  which  were  previously 
known,  and  has  led  to  the  discovery  of  new  facts  of  great  im- 
portance to  nutrition  and  to  our  estimates  of  the  nutritive 
values  of  foods. 

Most  of  what  we  now  know  of  the  chemical  structure  of  any 
protein  is  comprised  in  the  statement  of  the  amounts  of  the 
different  amino  acids  which  it  yields  on  hydrolysis.  In  the 
follomng  table  are  brought  together  the  pubHshed  results  of 
hydrolyses  of  the  principal  proteins  of  a  number  of  typical 
food  materials :  — 


VALUE  AND  ECONOMY  OF  FOODS 


301 


(:jnu  nz^jg) 
sUisjaDxa 

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1-5 

16.1 

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Glycin     .     . 
Alanin     .     . 
Valin  .     .     . 
Leucin     .     . 
Prolin      .     . 
Phenylalanin 
Aspartic  acid 
Glutamic  acid 
Serin    . 

1! 

Histidin  . 
Arginin    . 
Lysin  .     . 
Ammonia 
Tryptophan 

.2  J 
H  < 


302  CHEMISTRY    OF    FOOD   AND   NUTRITION 

The  absence  of  glycin  from  the  products  of  hydrolysis  of  a 
protein  is  of  no  significance  as  regards  its  nutritive  value,  for 
we  know  that  this  amino  acid  is  produced  in  the  intermediary 
metabolism  of  protein  in  the  animal  body  —  presumably  from 
the  amino  acids  of  greater  molecular  weight.  When,  however, 
an  amino  acid  having  a  complex  and  characteristic  radicle 
(such  as  phenylalanin,  tyrosin,  histidin,  or  tryptophan)  is 
found  to  be  almost  or  entirely  absent,  doubt  is  thrown  upon 
tiie  abihty  of  the  protein  in  question  to  supply  everything 
needed  for  the  replacement  of  katabolized  body  protein. 
The  presence  of  all  of  these  amino  acids  in  measurable  quanti- 
ties in  casein,  and  the  general  similarity  of  casein  and  ovovitel- 
lin, are  in  accord  with  the  known  superiority  of  milk  and  eggs 
as  foods  for  supplying  the  materials  needed  for  body  tissue. 
On  the  other  hand,  it  has  long  been  known  that  gelatin  as  a 
sole  protein  food  does  not  sufiice  for  the  maintenance  of  nitro- 
gen equilibrium.  When  the  development  of  protein  chemistry 
had  shown  that  gelatin  differs  from  most  other  proteins  in 
yielding  on  hydrolysis  no  tyrosin  or  tryptophan  and  little  if 
any  cystin,  Kauffmann  ^  tried  the  experiment  of  living  upon  a 
diet  in  which  these  three  amino  acids  were  eaten  along  with 
gelatin,  no  other  protein  being  taken,  and  found  that  nitrogen 
equilibrium  was  maintained  throughout  the  five  days  that 
this  diet  was  continued.  Recently  it  has  been  found  that  zein 
as  a  sole  source  of  nitrogen  cannot  maintain  growth  in  young 
mice,  and  it  is  believed  that  protein  equilibrium  cannot  be 
1  Tigerstedt's  Textbook  of  Physiology,  p.  109. 


VALUE  AND  ECONOMY  OF  FOODS        303 

supported  by  a  diet  devoid  of  the  tryptophan  group.  A  diet 
in  which  tryptophan  was  added  to  zein  gave  much  better 
results  than  one  in  which  the  nitrogen  was  suppUed  by  zein 
alone.^ 

Thus  the  proximate  analysis  of  a  food  may  be  extended 
much  beyond  the  scope  of  the  usual  routine  analysis  with 
correspondingly  increased  worth  as  a  basis  for  judgment  of 
nutritive  value.  It  has  been  pointed  out  in  the  preceding 
chapter  that  a  more  thorough  knowledge  of  the  ultimate 
composition,  such  as  is  gained  by  the  quantitative  determina- 
tion of  the  individual  ash  constituents,  has  also  important 
bearings  upon  our  judgment  of  nutritive  values. 

BEHAVIOR  IN  DIGESTION 

Discussion  of  the  behavior  of  a  food  in  digestion  should 
include  consideration  both  of  the  digestibility  of  the  food 
and  the  influence  of  the  food  upon  the  digestive  process.  The 
latter  subject  is  usually  treated  as  belonging  to  general 
physiological  chemistry  rather  than  specifically  to  nutrition ; 
but  certainly  our  judgments  of  the  nutritive  values  of  foods 
will  often  be  too  narrow  if  they  fail  to  take  account  of  the 
differences  which  exist  among  the  articles  of  food  as  regards 
their  influence  in  stimulating  or  retarding  the  flow  of  the 
digestive  juices,  the  rate  of  discharge  of  the  food  from  the 
stomach,  the  peristaltic  activity  of  the  intestine,  and  perhaps 

1  Willcock  and  Hopkins,  Journal  of  Physiology,  35,  88,  103  (1907) ; 
Chemical  Abstracts,  i,  600. 


304  CHEMISTRY    OF    FOOD    AND   NUTRITION 

other  less  obvious  ways  in  which  the  digestive  process  is  in- 
fluenced by  the  bulk,  flavor,  mechanical  condition,  and 
characteristic  chemical  constituents  of  the  food. 

In  studying  the  digestibility  of  a  food  one  may  employ 
either  natural  or  artificial  digestion,  i.e.  the  food  may  be 
actually  fed  to  a  man  or  other  animal,  or  it  may  be  treated 
with  a  digestive  solution  outside  of  the  body.  Such  arti- 
ficial experiments  have  been  applied  more  particulariy  to 
the  study  of  the  digestibiUty  of  protein,  the  food  being 
treated  sometimes  with  an  acid  solution  of  pepsin  (an  arti- 
ficial gastric  juice)  alone,  and  sometimes  first  with  such  a 
solution  and  then  with  an  alkaline  solution  of  trypsin,  in 
imitation  of  the  pancreatic  juice.  As  a  rule  these  artificial 
digestion  experiments  are  only  partially  satisfactory  sub- 
stitutes for  the  natural  digestion  test,  but  in  some  cases  the 
artificial  experiment  gives  information  which  would  not  be 
obtained  by  the  method  of  actual  feeding.  Thus  Grindley 
in  one  series  of  trials  found  no  apparent  effect  of  different 
methods  of  cooking  meats  upon  the  coefficients  of  digesti- 
bility when  fed  to  healthy  men,  but  by  subjecting  the 
samples  of  differently  cooked  meat  to  the  action  of  arti- 
ficial gastric  juice  for  Umited  periods  of  time,  and  compar- 
ing the  amounts  digested  after  certain  definite  intervals, 
he  found  the  lightly  cooked  samples  more  rapidly  di- 
gested than  the  same  meat  fried,  although  when  all  were 
allowed  to  digest  for  twenty-four  hours  the  differences 
tended  to  disappear. 


m 


VALUE  AND  ECONOMY  OF  FOODS 


305 


Grindley's  Summary  of  Results  of  Artificial  Digestion  Experi- 
ments WITH  Raw  and  Cooked  Beef  (U.  S.  Dept.  Agriculture, 
Office  of  Experiment  Stations,  Bull.  193,  p.  75) 


Description  of  Sample 

Percentage  Dissolved  by  Artificial  Digestive 
Gastric  Juice  During  — 

I  hour 

2  hours 

6  hours 

24  hours 

Lean  beef,  round,  raw  .  . 
Lean  beef,  round,  pan  broiled 
Lean  beef,  fried  in  hot  lard  . 
Lean  beef,  cooked  in  water  2 

hours 

Lean  beef,  round,  cooked  in 

water  5  hours      .... 

66.69 
78.41 
67.69 

85-74 
76.12 

79-54 
88.04 

80.45 
93-09 
81.73 

90.50 
92.87 
91.14 

96.35 
95-32 

97-31 
95-49 
95-07 

97-44 

96.95 

Somewhat  similar  comparisons  of  rapidity  of  digestion 
can  be  made  by  feeding  test  meals,  and  after  a  definite  inter- 
val withdrawing  and  examining  the  stomach  contents;  but 
such  tests  can  hardly  be  made  so  strictly  quantitative  as  are 
the  artificial  digestion  experiments  in  which  the  undigested 
residue  is  accurately  determined. 

Another  method  of  studying  rapidity  of  actual  digestion 
is  to  withdraw  the  partially  digested  food  mass  from  the 
stomach  or  intestine  through  a  fistula,  but  this  is  obviously 
of  rather  limited  application. 

Formerly  the  digestibility  of  a  food  was  studied  by  feeding 
that  food  alone  for  a  period  of  days,  marking  the  feces  be- 
longing to  this  period  by  taking  lampblack  at  the  beginning 
and  end  or  by  some  other  method,  and  comparing  the  con- 

X 


306  CHEMISTRY    OF    FOOD    AND   NUTRITION 

stituents  of  the  food  w-ith  those  of  the  corresponding  feces. 
It  is  now  recognized  that  such  "coefficients  of  digestibihty " 
do  not  measure  the  digestibility  of  the  food  in  a  literal  sense, 
but  do  give  valuable  indications  as  to  the  availability  of  its 
organic  constituents  for  metabolism  as  explained  in  Chapter 
III ;  and  that  they  should  be  determined  by  feeding  the  sub- 
stance under  investigation  not  as  the  sole  food,  but  as  a  con- 
siderable part  of  a  simple  mixed  diet,  the  digestibility  of 
whose  other  constituents  is  already  known.  To  what  ex- 
tent it  is  important  that  the  experimental  diet  should  be 
relished  by  the  subject  is  a  matter  of  considerable  doubt. 
The  brilliant  work  of  Pawlow  and  his  students  upon  the 
susceptibility  of  the  digestive  glands  to  psychic  influences 
such  as  those  which  obtain  in  "sham  feeding"  experiments 
appear  to  support  the  popular  belief  that  the  enjoyment  of 
the  food  is  a  very  important  factor  in  securing  its  proper 
digestion;  but  the  data  of  quantitative  digestion  experi- 
ments upon  healthy  men  afford  little,  if  any,  evidence  in 
support  of  this  view  and  much  evidence  that  the  coefficient 
of  digestibiHty  is  but  little  influenced  by  the  palatability  of 
the  food,  or  the  monotony  of  a  uniform  diet,  so  long  as  the 
food  is  actually  eaten  and  retained  and  does  not  undergo 
excessive  bacterial  decomposition.  Continuance  of  a  diet 
of  crackers  and  milk  alone  for  12  days,  and  in  another  case 
for  18  days,  resulted  in  no  diminution  of  the  coefficient 
of  digestibility,  and  in  a  series  of  experiments  in  which  the 
diet   consisted    largely   of    unpalatable    so-called    "canned 


VALUE  AND  ECONOMY  OF  FOODS        307 

roast  beef  "  which  could  be  eaten  only  by  considerable  effort, 
the  coefficient  of  digestibility  of  the  protein  of  this  beef  was 
found  to  be  92  per  cent,  while  the  protein  of  good  fresh  beef 
eaten  as  part  of  a  well-relished  diet  shows  about  97  or  98 
per  cent.  In  view  of  the  fact  that  the  extractives  which  are 
known  to  be  highly  efficient  in  stimulating  the  flow  of  gastric 
juice  had  been  largely  removed  from  the  "canned  roast 
beef,"  and  that  the  amount  of  beef  eaten  was  larger  than 
would  have  been  desired  in  any  case,  it  would  seem  that  but 
little  depression  of  the  coefficient  of  digestibility  can  be 
attributed  directly  to  the  lack  of  enjoyment  of  the  food. 
It  seems  probable  that  the  psychic  influences  affect  the 
comfort  and  rapidity  of  the  earlier  stages  of  digestion  much 
more  than  the  final  percentage  utilization  of  the  food. 

The  term  "digestibility"  of  food  may  mean  either  the 
ease  and  comfort,  or  the  rapidity,  or  the  ultimate  extent  of 
its  digestion.  Foods  which  differ  in  their  susceptibility  to 
natural  or  artificial  gastric  juice  or  in  the  rapidity  with  which 
they  leave  the  stomach  may  still  show  an  equally  complete 
digestion  and  absorption  by  the  time  they  have  passed 
through  the  intestine.  On  the  other  hand,  the  "coefficient 
of  digestibihty,"  which  is  simply  a  measure  of  the  quantitative 
difference  between  food  and  feces,  does  not  necessarily  in- 
dicate the  ease  or  rapidity  of  digestion,  nor  the  extent  to 
which  the  foodstuffs  which  appear  to  have  been  absorbed 
may  have  been  decomposed  by  the  bacteria  of  the  digestive 
tract. 


3c8 


CHEMISTRY    OF    FOOD    AND    NUTRITION 


BEHAVIOR   IN   METABOLISM 

Foods  similar  in  chemical  composition  and  equally  well 
digested  may  or  may  not  be  of  equal  nutritive  value. 

Rutgers,  in  1887,  compared  animal  and  vegetable  protein 
by  substituting  beans  and  peas  for  the  meat  of  a  mixed  diet 
which  was  so  arranged  as  to  keep  the  amounts  of  proteins, 
fats,  and  carbohydrates  uniform.  Each  diet  was  continued 
for  several  weeks  with  determinations  of  the  nitrogen  balance 
on  certain  days,  and  the  conclusion  was  reached  that  the 
protein  of  the  legumes  was  equal  in  nutritive  value  to  the 
meat  protein  which  it  displaced.  The  conclusion  reached 
in  this  comparatively  early  work  accords  well  with  our  pres- 
ent knowledge  of  the  similarity  of  cleavage  products  of  the 
meat  and  legume  proteins  (see  table  above). 

Data  obtained  by  Neumann  in  examining  two  commercial 
protein  preparations  illustrate  the  fact  that  foods  which 
appear  similar  as  ordinarily  analyzed  may  differ  in  their 
behavior  either  in  digestion  or  in  metabolism.  These  pro- 
tein preparations  were  fed  in  a  simple  mixed  diet  alternat- 
ing with  meat  in  such  quantities  as  to  maintain  uniformity 
of  nitrogen  content  and  fuel  value  in  the  diet. 

The  results  were  as  follows :  — 


Period 

Duration 
Days 

Principal 
Protein 
of  Food 

Nitrogen  in  Grams  per  Day 

No. 

In  food 

In  feces 

In  urine 

Balance 

I 
2 
3 
4 
5 

4 
8 

S 

Meat 
Food  A 
Meat 
FoodB 
Meat 

14.02 
14.02 
14.02 
14.02 
14.02 

2.06 
2.14 
2.17 

3-14 
2.26 

12.09 
14.49 
12.25 
12.29 
12.30 

-0.13 

-  2.61 

-  0.40 

-  1.41 
-0.54 

VALUE  AND  ECONOMY  OF  FOODS        309' 

Here  both  of  the  proprietary  protein  foods  proved  inferior 
in  nutritive  value  to  meat,  one  because  of  the  greater  amount 
of  nitrogen  in  the  feces  (less  favorable  digestion),  the  other 
because  of  the  greater  amount  of  nitrogen  in  the  urine  (less 
favorable  metabolism). 

In  experiments  of  this  sort  care  must  be  taken  that  the 
fuel  value  is  the  same  in  the  periods  for  which  the  nitrogen 
balance  is  to  be  compared,  as  otherwise  the  protein-sparing 
action  of  the  carbohydrates  and  fats  may  vitiate  the  results. 
In  fact,  it  is  by  means  of  nitrogen  balance  experiments  that 
the  protein-sparing  powers  of  fats  and  carbohydrates  were 
studied  and  compared,  and  the  data  of  some  of  these  in- 
vestigations have  been  given  in  Chapter  VII. 

The  nutritive  value  of  non-nitrogenous  foodstuffs  may 
also  be  studied  in  a  more  direct  way  by  means  of  the  carbon 
or  energy  balance  and  in  some  instances  by  searching  for 
evidence  of  the  absorbed  material,  as,  for  example,  by  an 
increased  storage  of  glycogen,  by  a  change  in  the  respiratory 
quotient,  or  (in  the  case  of  a  carbohydrate)  by  elimination  of 
the  substance  or  its  products  of  hydrolysis  in  the  urine  after 
phloridzin  poisoning. 

The  following  instances  of  investigations  of  different  car- 
bohydrates will  illustrate  the  application  of  some  of  these 
methods  of  study. 

Weiske  ^  fed  carob  beans  (which  consist  largely  of  mannan) 
with  hay  to  sheep  in  comparison  with  a  ration  of  starch  and 

^Journal  fiir  LandwirtJischaft,  27,  321. 


3IO  CHEMISTRY    OF   FOOD    AND   NUTRITION 

hay,  and  found  such  similar  data  of  digestibihty  and  nitro- 
gen balance  as  to  show  that  the  mannan  was  well  utilized. 
Oshima  ^  cites  an  experiment  with  man  in  which  the  digesti- 
bility of  konnyaku,  consisting  mainly  of  mannan,  was 
found  to  be  82  per  cent.  Sawamura  ^  has  found  a  mannose 
in  the  digestive  tracts  of  horses  and  swine,  and  it  is  known 
that  mannose  is  well  utilized  in  the  animal  organism  so  that ; 
the  nutritive  value  of  at  least  some  of  the  forms  of  mannan 
is  fairly  well  established. 

On  the  other  hand,  studies  of  inulin  do  not  afford  corre- 
sponding evidence  of  utilization.  Although  inulin  is  readily 
hydrolyzed  to  levulose  by  acids,  it  is  not  attacked  by  the 
saliva  or  pancreatic  juice.  Sandmeyer^  after  feeding  80 
grams  of  inulin  to  a  diabetic  dog  recovered  46  grams  in  the 
feces,  and  Mendel  and  Nakaseko  *  found  that  little  if  any 
glycogen  resulted  from  feeding  inulin  to  a  rabbit.  Mendel 
and  Mitchell  ^  further  find  that  most  of  the  inulin  injected 
peritoneally  can  be  recovered  in  the  urine. 

Galactans,  as  Mendel  and  Swartz  have  pointed  out,  are 
as  a  rule  very  incompletely  digested,  and,  being  at  the  same 
time  resistant  to  bacteria  and  retentive  of  water  in  the  in- 

1  U.  S.  Dept.  Agriculture,  Office  of  Experiment  Stations,  Bull.  159, 
pp.  35,  168,  173. 

2  Bulletin  College  Agriculture,  Tokyo  Imperial  Univ.,  No.  5,  p.  155  ; 
Swartz,  Dissertation,  Yale,  1909. 

^  Zeitschrift  fur  Biologic,  31,  32  (1895). 
^American  Journal  of  Physiology ^  4,   246. 
^  Ibid.,  14,  239. 


VALUE  AND  ECONOMY  OF  FOODS        311 

testine,  they  are  useful  in  the  food  in  cases  of  chronic  con- 
stipation, particularly  when  this  is  due  to  the  extremely 
complete  absorption  of  the  food  (and  its  accompanying 
moisture)  and  the  consequent  formation  of  hard,  dry  fecal 
masses.  Some  forms  of  galactan  are,  however,  fairly  well 
absorbed,  and  in  three  experiments  Lohrisch  found  a  rise  of 
the  respiratory  quotient  three  or  four  hours  after  eating 
galactan,  indicating  a  metabolism  of  the  absorbed  carbo- 
hydrate. 

Lohrisch  ^  also  studied  the  question  of  the  utilization  of 
cellulose.  When  healthy  men  ate  the  tender  cellulose  of 
white  cabbage,  practically  none  of  it  was  found  in  the  feces, 
but  on  adding  the  same  form  of  cellulose  to  the  diet  of 
diabetics,  no  increase  of  the  sugar  in  the  urine  was  found. 
Lohrisch  then  determined  the  respiratory  quotient  before, 
and  at  hourly  intervals  after,  eating  76  grams  of  cellulose 
of  which  one  fourth  was  apparently  digested.  Four  hours 
after  the  cellulose  was  eaten  there  was  a  slight  rise  in 
the  respiratory  quotient,  after  which  it  gradually  decreased 
and  remained  for  some  hours  at  about  0.7.  Lohrisch 
interprets  these  results  as  indicating  first  a  utilization  of  a 
part  of  the  cellulose  as  carbohydrate  and  later  a  utiUzation 
of  fatty  acids  derived  from  the  cellulose  —  presumably  by 
bacterial  decomposition  in  the  intestine.  It  should  be 
noted,  however,  that  the  rise  of  respiratory  quotient  ob- 

^  Zeitschrift  physiologische  Chemie,  47  (1907) ;  through  Swartz,  Dis- 
sertation, Yale,  1909. 


312 


CHEMISTRY    OF   FOOD    AND   NUTRITION 


served  by  Lohrisch  in  this  case  was  no  greater  than  may 
occur  in  the  accidental  fluctuations  from  hour  to  hour. 

Experiments,  such  as  have  here  been  cited,  upon  the  utiU- 
zation  of  the  organic  nutrients  have  to  do  with  the  values 
of  foods  as  sources  of  energy  and  protein,  but  these  alone  do 
not  furnish  a  complete  measure  of  nutritive  value.  This  is 
illustrated  by  the  following  data  of  two  metaboHsm  experi- 
ments with  the  same  man  upon  diets  which  furnished  about 
the  same  fuel  value  and  protein. 


Comparison  of  Balances  of  Different  Elements 


AMOtJNT  IN  Grams  per  Day 

In  food 

In  feces 

In  lu-ine 

Balance 

Bread  and  milk 

Nitrogen 

lO.IO 

0.46 

13.09 

-3-45 

Bread    and    egg 

white     .     .     . 

Nitrogen 

10.69 

.75 

13.21 

-3.27 

Bread  and  milk  . 

Phosphorus 

1.55 

•57 

1.03 

—  0.05 

Bread    and    egg 

white    .     .     . 

Phosphorus 

0.38 

.22 

•75 

-0.59 

Bread  and  milk . 

Calcium  oxide 

2.65 

1.88 

.21 

+  0.56 

Bread   and   egg 

white    .     .     . 

Calcium  oxide 

0.14 

.48 

.10 

-0.44 

Bread  and  milk . 

Iron 

0.0057 

.0053 

.0002 

+  .0002 

Bread    and    egg 

white    .     .     . 

Iron 

0.0065 

.0085 

.0002 

-  .0022 

Here,  although  the  nitrogen  balance  was  practically  alike 
on  the  two  diets,  there  was  on  the  bread  and  milk  diet  prac- 


VALUE  AND  ECONOMY  OF  FOODS        313 

tical  equilibrium  of  phosphorus  and  iron  and  a  storage  of 
calcium,  while  on  the  diet  of  bread  and  egg  white  there  were 
relatively  large  losses  of  all  three  of  these  elements. 

Reference  may  be  made  to  Chapters  IX  and  X  for  the 
reasons  for  particularly  considering  these  three  elements,  and 
also  for  examples  of  investigations  in  which  the  nutritive 
values  of  rations  have  been  studied  by  long-continued  feed- 
ing experiments  instead  of  by  the  direct  determination  of 
intake  and  output.  Further  examples  may  be  found  in 
the  works  of  Forbes  and  of  Watson  and  Hunter  which 
are  included  among  the  references  at  the  end  of  this 
chapter. 

Even  these  experiments  upon  growth  and  development, 
however,  may  not  always  exhaust  the  question  of  nutritive 
value  in  the  broadest  sense.  Hunt  has  recently  found  great 
differences  in  the  resistance  of  animals  to  certain  poisons, 
which  appear  to  be  attributable  to  diet  alone. 

"In  extreme  cases  mice  after  having  been  fed  upon  certain 
diets  may  recover  from  forty  times  the  dose  of  acetonitrile 
fatal  to  mice  kept  upon  other  diets.  It  is,  moreover,  possible 
to  alter  the  resistance  of  these  animals  at  will  and  to  over- 
come the  effects  of  one  diet  by  combining  it  with  another. 
.  .  .  The  experiments  with  oats  and  oatmeal  and  eggs 
are  of  especial  interest.  In  the  earher  parts  of  this  paper 
many  experiments  were  quoted  showing  that  a  diet  of  oat- 
meal or  of  oats  usually  leads  to  a  marked  resistance  of 
mice  to  acetonitrile;  the  experiments  quoted  in  this  section 


314  CHEMISTRY    OF   FOOD   AND   NUTRITION 

which  show  that  the  administration  of  certain  iodine  com- 
pounds with  or  subsequently  to  such  a  diet  further  in- 
creases this  resistance,  and  the  experiments  previously- 
reported  showing  that  as  far  as  the  resistance  toward 
acetonitrile  is  concerned  iodine  exerts  its  action  through  the 
thyroid  gland,  all  point  to  the  conclusion  that  the  resistance 
caused  by  an  oat  diet  is  in  part  an  effect  exerted  upon  the 
thyroid.  This  effect  is  obtained  much  more  markedly  and 
constantly  with  young,  growing  mice.  From  these  experi- 
ments and  considerations  it  seems  very  probable  that  it 
is  possible  to  influence,  in  a  specific  manner,  by  diet,  one 
of  the  most  important  hormones  in  the  body;  this  is  a 
comparatively  new  principle  in  dietetics  and  one  which 
may  prove  of  much  importance."  {The  Effect  of  a  Re- 
stricted Diet  and  oj  Various  Diets  upon  the  Resistance  of 
Animals  to  Certain  Poisons^  pp.  56,  73.) 

COMPARATIVE  ECONOMY  OF  FOODS 

In  studying  the  economy  of  an  article  of  food  we  may 
well  consider  first  its  cheapness  as  a  source  of  fuel.  Using 
prices  now  or  recently  current  in  the  retail  markets  of  New 
York  City  and  the  fuel  values  given  in  Bulletin  28  of  the 
OflSce  of  Experiment  Stations,  we  find  the  cost  of  3000  calories 
from  any  one  of  a  number  of  typical  food  materials  to  be 
approximately  as  follows:  — 


VALUE  AND  ECONOMY  OF  FOODS 


315 


Food 

Price  per  Pound 

Cost  of  3cx» 
Calories 

Flour 

Oatmeal 

Sugar    

Potatoes 

$0.04 
.06 
.06 
.01^  (.00  Dcr  bu.) 

$0.08 
.10 
.10 
.14 
.15 
•15 
.16 
.24 
.27 
.28 
.30 
•30 
.28 
'33 
•33 
•37 
.40 
.46 
.60 
.88 

I-I3 
1.26 
1.90 

Bread 

Beans,  dried  ...'... 

Clear  fat  pork 

Potatoes 

.06 
.08 

.20 

Bacon 

Milk 

Raisins,  seeded 

Prunes,  dried 

Shredded  wheat      .... 

Butter 

Evaporated  apples      .     .     . 

Milk 

Olive  oil 

Milk 

Almonds  (without  shell)  .     . 
Round  steak,  fat  eaten    .     . 

Eggs 

Round  steak,  fat  not  eaten  . 
Oysters  (without  shell)     .     . 

•25 

.03  (.06  qt.) 

•IS 
.12 
.16 
.40 

•IS 

.04  (.08  qt.) 

•55 

.05  (.10  qt.) 

.60 

.20 
.24  (.35  doz.) 

.20 
.15  (.30  qt.) 

-    The  differences  in  economy  of  staple  articles  of  food  com- 
pared on  this  basis  are  seen  to  be  enormous. 

These  estimates  are  based  upon  the  fuel  values  found  by 
applying  average  factors  to  the  data  of  ordinary  proximate 
analyses,  and  do  not  take  account  of  the  different  forms  of 
proteins,  fats,  and  carbohydrates  present  in  the  different 


3l6  CHEMISTRY    OF   FOOD    AND    NUTRITION 

foods,  or  of  their  differences  of  behavior  in  digestion  and  in 
metabolism,  such  as  have  been  referred  to  in  this  chapter. 
If  our  comparisons  of  nutritive  value  are  to  be  adequate,  it 
is  evident  that  all  such  factors  should  be  taken  into  consid- 
eration along  with  the  fact  that  the  food  while  used  pri- 
marily as  fuel  must  also  furnish  the  necessary  elements  of 
building  material,  among  which,  according  to  our  present 
knowledge,  nitrogen,  phosphorus,  iron,  and  calcium  appear 
to  require  especial  consideration.  This  broader  conception  of 
nutritive  value  supplies  the  economic  justification  for  the  pur- 
chase of  certain  foods  which  would  appear  expensive  if  con- 
sidered simply  as  sources  of  proteins,  fats,  and  carbohydrates, 
and,  on  the  other  hand,  some  foods  which  are  economical 
sources  of  protein  and  energy  are  also  of  high  nutritive 
value  in  other  respects. 

Making  due  allowance  for  all  known  factors  which  affect 
the  nutritive  values  of  foods,  there  remain  large  discrepancies 
between  nutritive  value  and  market  cost  and  correspondingly 
ample  opportunity  for  the  exercise  of  true  economy  in  the 
choice  of  food  materials. 

REFERENCES 

Abderhalden.    Handbuch  der  Biochemischen  Arbeitsmethoden,  Bd. 

Ill  (1910). 
Atwater.     Methods  and  Results  of  Investigation  on  the    Chemistry 

and  Economy  of  Food.     Bull.  21,  Office  of  Experiment  Stations,  U.  S. 

Dept.  Agriculture  (1895). 
Atwater.     Neue  Versuche  ueber  Stoff-  und  Kraftwechsel  im  mensch- 

lichen  Korper.    Ergehnisse  der  Fhysiologie,  3,  I,  497-604  (1904). 


VALUE  AND  ECONOMY  OF  FOODS        317 

Atwater  and  Langworthy.     a  Digest   of  Metabolism  Experiments. 

Bull.  45,  OflBce  of  Experiment  Stations,  U.  S.    Dept.  Agriculture 

(1898). 
Forbes.     Specific  Effects  of  Rations  upon  the  Development  of  Swine. 

Bull.  213,  Ohio  Agricultural  Experiment  Station,  Wooster,  Ohio, 

1909. 
Hunt.     The  Effects  of  a  Restricted  Diet  and  of  Various  Diets  upon  the 

Resistance   of    Anirhals  to    Certain  Poisons.     Bull.  69,    Hygienic 

Laboratory,  U.  S.  Treasury  Department,  1910. 
LusK.     Elements  of  the  Science  of  Nutrition,  2d  ed.,  1909. 
Mendel  and  Swartz.    The  Physiological  Utilization  of  Some  Complex 

Carbohydrates.     American  Journal  of  the  Medical  Sciences,  March, 

1910. 
MuRLiN.    The  Nutritive  Value  of  Gelatin.  American  Journal  of  Physiol- 
ogy, 19,  285-313;   20,  234-258  (1907-1908). 
Neumann.    Die  Wirkung  des  Alkohols  als  Eiweiss-sparer.    Archiv  fiir 

Hygiene,  41,  85-118  (1902). 
Reitz  and  Mitchell.     On  the  MetaboHsm  Experiment  as  a  Statistical 

Problem.    Journal  of  Biological  Chemistry,  8,  297-326  (1910). 
Rutgers.     Haben  vegetabilisches  Eiweissstoffe  den  gleichen  Nahrwerth 

fiir  Menschen  wie  die  AnimaUschen  ?     Zeitschrift  fiir  Biologic  (N. 

f.),  6,  351-381  (1888). 
Staehelin.     (Physiological  effects  of  vegetarian  diet  with  bibliography.) 

Zeitschrift  fiir  Biologic  (N.  f.),3i,  199-263. 
Tallquist.     Zur  Frage  des  Einflusses  von  Fett  und  Kohlenhydrat  auf 

den  Eiweiss-umsatz  des  Menschen.     Archiv  JUr  Hygiene,  41,  1 77-189 

(1902). 
VoiT  AND  Zisterer.     Bedingt  die  verscheidene  Zusammensetzung  der 
'        Eiweisskorper  auch  einen  Unterscheid  in  ihrem  Nahrwert  ?     Zeit- 
schrift fiir  Biologie  (N.  f.),  35,  457-498  (1910). 
Von  Noorden.     Grundriss  einer  Methodik  der  Stoffwechsel-Untersuch- 

ungen.     Berlin,  1892. 
Watson  and  Hunter.    Observations  on  Diet.    The  Influence  of  Diet 

on  Growth  and  Nutrition.     Journal  of  Physiology,  34,  111-132 

(1906). 
WiLLCOCK  AND  HoPKiNS.    The  Importance  of  Individual  Amino  Acids 

in  Metabolism.    Journal  of  Physiology,  35,  88-102  (1906). 


SUk 


APPENDIX 


TABLE  I 

Edible  Organic  Nutrients  and  Fuel  Values  of  Foods  ^• 


Food 


Almonds 2  g.  P. 

2  A.  P. 
Apples E.  P. 

A.  P. 
Apricots E.  P. 

A.  P. 
Asparagus,  fresh      .     .     .A.  P. 

cooked A,  P. 

Bacon,  smoked    ,     .     .     .  E.  P. 

A.  P. 
Bananas E.  P. 

A.  P. 
Barley,  pearled    .... 

Beans,  dried 

lima,  dried 


Protein 

(NX6.25) 

PER  CENT 

Fat 

PER 

CENT 

Carbo- 
hy- 
drate 

PER 

CENT 

Fuel 
Value 

PER 

Pound 
Calo- 
ries 

21.0 

54-9 

17-3 

2940 

II-5 

30.2 

9-5 

1615 

•4 

.5 

14.2 

28s 

•3 

•3 

10.8 

214 

I.I 

134 

263 

I.O 

12.6 

247 

1.8 

.2 

3-3 

100 

2.1 

3-3 

2.2 

213 

10.5 

64.8 

2840 

9-5 

59-4 

2372 

1-3 

.6 

22.0 

447 

.8 

.4 

14-3 

290 

8.5 

I.I 

77.8 

1615 

22.5 

1.8 

59-6 

1565 

18.1 

i-S 

65-9 

1586 

100 

Calorie 

Portion 

Grams 


15 
28 

159 
212 

174 
184 
450 
213 
16 

19 

lOI 

156 
28 

29 
29 


^The  percentages  of  nutrients  are  taken  from  Bull.  28,  Office  of  Ex- 
periment Stations,  U.  S.  Department  of  Agriculture.  The  fuel  values 
are  calculated  from  these  percentages  by  the  use  of  the  factors  explained 
in  Chapter  V,  viz.  —  protein,  4  calories  ;  fat,  9  calories  ;  carbohydrate,  4 
calories  per  gram. 

2  E.  P.  signifies  edible  portion ;  A.  P.  signifies  as  purchased. 

319 


320 


APPENDIX 
TABLE  I,  continued 


Food 

Protein 
(NX6.2S) 

Fat 

PER 

Carbo- 
hy- 
drate 

Fuel 
Value 

PER 

Pound 

100 
Calorie 
Portion 

PER    CENT 

CENT 

PER 

cent 

Calo- 
ries 

Grams 

lima,  fresh  .... 

.  E.  P. 

7-1 

•7 

22.0 

557 

82 

A.  P. 

,3-2 

•3 

9.9 

250 

182 

string,  fresh     .     .    . 

.  E.  P. 

2.3 

•3 

7-4 

184 

241 

A.  P. 

2.1 

•3 

6.9 

176 

259 

baked,  canned      .    . 

.  A.  P. 

6.9 

2.5 

19.6 

583 

78 

string,  canned       .     . 

A.  P. 

I.I 

.1 

3-8 

93 

488 

lima,  canned    .     .     . 

A.  P. 

4.0 

•3 

14.6 

350 

130 

Beef  brisket,  medimn  fat 

E.  P. 

15-8 

28.5 

1449 

31 

A.  P. 

12.0 

22.3 

1130 

40 

chuck,  average     .     . 

E.  P. 

19.2 

iS-4 

978 

46 

A.  P. 

15.8 

12.5 

797 

58 

corned,  average    .     . 

E.  P. 

15.6 

26.2 

1353 

34 

A.  P. 

14-3 

23.8 
58.2 

1230 

37 

cross  ribs,  average    , 

E.  P. 

159 

1440 

32 

A.  P. 

13-8 

24.8 

1262 

36 

dried,  salted,  and  smoked  E,  P. 

30.0 

6.5 

•4 

817 

56 

A.  P. 

26.4 

6.9 

724 

63 

flank,  lean  .... 

E.  P. 

20.8 

II-3 

838 

54 

A.  P. 

20.5 

II.O 

821 

55 

fore  quarter,  lean 

.  E.  P. 

18.9 

12.2 

842 

54 

A.  P. 

14.7 

9-5 

655 

69 

fore  shank,  lean   .     . 

E.  P. 

22.0 

6.1 

647 

70 

A.  P. 

14.0 

3-9 

414 

no 

heart      

.  E.  P. 

16.0 

20.4 

I.O 

1 140 

40 

A.  P. 

14.8 

24.7 

•9 

1292 

35 

hind  quarter,  lean     . 

.  E.  P. 

20.0 

13-4 

907 

50 

A.  P. 

16.7 

II. 2 

757 

60 

hind  shank,  lean      .     . 

E.  P. 

21.9 

5-4 

617 

75 

A.  P. 

9.1 

2.2 

255 

179 

APPENDIX 
TABLE  I,  continued 


321 


Food 


hind  shank,  fat     .     .     .  E.  P. 

A.  P. 
liver E.  P. 

A.  P. 
loin E.  P. 

A.  P. 
neck,  lean E.  P. 

A.  P. 
neck,  medium  fat      .     .  E.  P. 

A.  P. 
plate,  lean E.  P. 

A.  P. 
porterhouse  steak     .     .  E.  P. 

A.  P. 
rib  rolls,  lean  .  .  .  .  A.  P. 
ribs,  lean     .    .     .     .     .  E.  P. 

A.  P. 
ribs,  fat E.  P. 

A.  P. 

roast A.  P. 

round,  lean      .     .     .     .  E.  P. 

A.  P. 
round,  free  from  visible  fat 
rump,  lean     .     .     .     .    E.  P. 

A.  P. 
rump,  fat    .     .     .     .     .  E.  P. 

A.  P. 
sides,  lean E.  P. 

A.  P. 


Protein 
(Nx6.2s) 

PERCENT 

Fat 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 
CENT 

Fuel 
Value 

PER 

Pound 
Calo- 
ries 

100 
Calorie 
Portion 
Grams 

20.4 

18.8 

I171 

40 

9.9 

9.1 

552 

83 

20.4 

4-5 

1.7 

584 

78 

20.2 

3.1 

2.5 

537 

85 

19.7 

12.7 

877 

52 

I7.I 

II. I 

764 

60 

21.4 

8.4 

732 

62 

iS-i 

5-9 

493 

93 

20.1 

16.5 

1040 

44 

14-5 

11.9 

749 

61 

15.6 

18.8 

1051 

43 

13-0 

15-5 

867 

52 

21.9 

20.4 

1230 

37 

19.1 

17.9 

1077 

42 

20.2 

10.5 

795 

57 

19.6 

12.0 

845 

54 

15.2 

9-3 

654 

69 

15-0 

35-6 

1721 

26 

12.7 

30.6 

1480 

3^ 

22.3 

28.6 

1576 

29 

21.3 

7-9 

694 

64 

19-5 

7-3 

649 

70 

23.2 

2-5 

512 

87 

20.9 

13-7 

940 

49 

19. 1 

II.O 

796 

57 

16.8 

35-7 

1763 

26 

12.9 

27.6 

1361 

33 

19-3 

13.2 

890 

51 

15-5 

10.6 

715 

64 

322 


APPENDIX 
TABLE  I,  continued 


Food 


sirloin  steak     .     .     .     .  E.  P. 

A.  P. 

sweetbreads     .     .     .     .  A.  P. 

tenderloin A.  P. 

tongue E.  P. 

A.  P. 
Beets,  cooked      .     .     .     .  E,  P. 

fresh       E.  P. 

A.  P. 

Blackberries A.  P. 

Blackfish E.  P. 

A.  P. 

Bluefish E.  P. 

A.  P. 
Boston  crackers  .... 

Brazil  nuts E.  P. 

A.  P. 
Bread,  graham    .... 
rolls,  water       .... 

toasted 

white,  homemade     .     . 
milk  ....... 

Vienna 

average 

whole  wheat    .... 
Buckwheat  flour      .     .     . 

Butter 

Buttermilk 

Butternuts E.  P. 


Protein 
(Nx6.25) 

PER 
CENT 

Fat 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 
CENT 

Fuel 
Value 

PER 

Pound    ] 
Calo- 
ries 

18.9 

18.5 

1099 

16.5 

I6.I 



960 

16.8 

12. 1 

799 

16.2 

24.4 

1290 

18.9 

9.2 

717 

I4.I 

6.7 

529 

2.3 

.1 

74 

180 

1.6 

.1 

9-7 

209 

1-3 

.1 

7.7 

167 

1-3 

1.0 

10.9 

262 

18.7 

1-3 

393 

7-4 

•7 

176 

19.4 

1.2 

402 

lO.O 

.6 

206 

II.O 

8.5 

71. 1 

1835 

17.0 

66.8 

7.0 

3040 

8.6 

33.7 

3-5 

1591 

8.9 

1.8 

52.1 

1 189 

9.0 

3-0 

54-2 

1268 

"5 

1.6 

61.2 

1385 

9.1 

1.6 

53-3 

1 199 

9.6 

1.4 

511 

1158 

9.4 

1.2 

54.1 

1 199 

9.2 

1-3 

S3-I 

1182 

9-7 

•9 

49-7 

1113 

6.4 

1.2 

77-9 

1580 

I.O 

85.0 

3491 

3-0 

•5 

4.8 

162 

27.9 

61.2 

3-5 

3065 

APPENDIX 
TABLE  I,  continued 


323 


Food 


Butternuts A.  P. 

Cabbage E.  P. 

A.  P. 
Calf  s-foot  jelly  .... 
Carrots,  fresh      .     .     .     .  E.  P. 
A.  P. 

Cauliflower A.  P. 

Celery E.  P. 

A.  P. 
Celery  soup,  canned     .     . 

Cerealine 

Cheese,  American  pale  .  . 
American  red  .... 

Cheddar 

Cottage 

Full  cream 

Fromage  de  Brie       .     . 

Neuchatel 

Pineapple 

Roquefort 

Swiss 

Cherries,  fresh    .     .     .     .  E.  P. 
A.  P. 

canned A.  P. 

Chestnuts,  fresh       .     .     .  E.  P. 

A.  P. 

Chicken,  broilers     .     .     .  E.  P. 

A.  P. 

Chocolate 


Protein 

(Nx6.2s) 

PER 
CENT 

Fat 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 
CENT 

Fuel 
Value 
per 
Pound 
Calo- 
ries 

3.8 

8.3 

•5 

417 

1.6 

•3 

5-6 

143 

1.4 

.2 

4.8 

121 

4-3 

17.4 

394 

I.I 

•4 

9-3 

204 

•9 

.2 

7-4 

158 

1.8 

•5 

4.7 

139 

I.I 

.1 

2>-2> 

840 

•9 

.1 

2.6 

676 

2.1 

2.8 

S-o 

243 

9.6 

I.I 

78.3 

1640 

28.8 

35.9 

.3 

1990 

29.6 

38.3 

2102 

27.7 

36.8 

4.1 

2080 

20.9 

1.0 

4-3 

499 

25-9 

33-7 

2.4 

1890 

15-9 

21.0 

1.4 

1 1 70 

18.7 

27.4 

1-5 

1484 

29.9 

38.9 

2.6 

2180 

22.6 

29-5 

1.8 

1645 

27.6 

34-9 

1-3 

1945 

I.O 

.8 

16.7 

354 

.9 

.8 

15-9 

337 

I.I 

'  .1 

21. 1 

407 

6.2 

5-4 

42.1 

1098 

5-2 

4-5 

35-4 

920 

2I.S 

2-5 

493 

12.8 

1.4 

289 

12.9 

48.7 

30.3 

2768 

100 
Calorie 
Portion 
Grams 


109 
317 
376 

"5 

221 
286 
328 
542 
672 
187 
28 

23 
22 
22 

91 

24 

39 

31 

'  21 

28 

23 
128 

134 
112 

43 
49 
92 
157 
16 


324 


APPENDIX 
TABLE  I,  continued 


Food 


Cocoa 

Cod,  dressed A.  P. 

salt E.  P. 

A.  P. 
Consomm^,  canned.     .     .  A.  P. 

Com,  green A.  P. 

Com  meal 

Cowi)eas,  dried   .... 

green E,  P. 

Crackers,  butter .     .     .     .  A.  P. 

cream A.  P. 

graham A.  P. 

soda A.  P. 

water A.  P. 

Cranberries A.  P. 

Cream 

Cucumbers E.  P. 

A.  P. 
Currants,  fresh    .... 

dried  Zante      .... 

Dates,  dried E.  P. 

A.  P. 

Doughnuts 

Eggplant E.  P. 

Eggs,  imcooked  .     .     .     .  E.  P. 
A.  P. 

Farina 

Figs,  dried 

Flounder A.  P. 


Protein 
(N  X  6.2S) 

PER 
CENT 

Fat 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 
CENT 

Fuel 
Value 
per 
Pound 
Calo- 

RTKS 

100 
Calorie 
Portion 
Grams 

21.6 

28.9 

37-7 

2258 

20 

II. I 

.2 

209 

217 

25-4 

•3 

473 

96 

19.0 

•4 

361 

126 

2-5 

.4 

53 

862 

2.8 

1.2 

19.0 

455 

102 

9.2 

1.9 

75-4 

1620 

28 

21.4 

1.4 

60.8 

1550 

29 

9.4 

.6 

22.7 

603 

76 

9.6 

lO.I 

71.6 

1887 

2i 

9-7 

12. 1 

69.7 

1938 

23 

lO.O 

9.4 

73-8 

1905 

24 

9.8 

9.1 

73-1 

1875 

24 

10.7 

8.8 

71.9 

1855 

24 

•4 

.6 

9.9 

212 

212 

2.5 

18.5 

4-5 

883 

50 

.8 

.2 

31 

79 

575 

.7 

.2 

2.6 

68 

666 

1-5 

12.8 

259 

175 

2.4 

1-7 

74.2 

1455 

31 

2.1 

2.8 

78.4 

1575 

29 

1.9 

2-5 

70.6 

1430 

32 

6.7 

21.0 

53-1 

1941 

23 

1.2 

.3 

S-i 

126 

349 

134 

10.5 

672 

68 

11.9 

9-3 

594 

76 

II.O 

1.4 

76.3 

1640 

28 

4-3 

•3 

74.2 

1437 

32 

5-4 

•3 

no 

412 

APPENDIX 
TABLE  I,  continued 


325 


Food 

Protein 
(NX6.2S) 

PER 
CENT 

Fat. 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 
CENT 

Fuel 
Value 

PER 

Pound 
Calo- 
ries 

100 

Calorie 

Portion 

Grams 

Flounder 

E.  P. 

14.2 

.6 

282 

161 

Flour,  rye 

6.8 

.9 

78.7 

1590 

29 

wheat,  California  fine    . 

7-9 

1.4 

76.4 

158s 

29 

wheat,  entire   .... 

13.8 

1.9 

71.9 

1630 

28 

wheat,  graham     .     .     . 

i3v^ 

2.2 

71.4 

1628 

28 

wheat,  patent  roller  process  ^ 

13-3 

1-5 

72.7 

1623 

28 

wheat,  straight  grade    . 

10.8 

I.I 

74.8 

1608 

28 

wheat,  average  high  and 

medium   ..... 

11.4 

1.0 

75-1 

1610 

28 

wheat,  average  low  grade 

14.0 

1.9 

71.2 

1625 

28 

Fowls 

E.  P. 

193 

16.3 

1017 

45 

A.  P. 

13-7 

12.3 

752 

60 

Gelatin 

91.4 

.1 

■ 

1660 

27 

Grape  butter 

1.2 

.1 

58.5 

1088 

42 

Grapes 

E.  P. 

1.3 

1.6 

19.2 

437 

104 

A.  P. 

I.O 

1.2 

14.4 

328 

138 

Haddock 

E.  P. 

17.2 
8.4 

•3 
.2 

324 
160 

140 

A.  P. 

283 

Halibut  steaks    .... 

E.  P. 

18.6 

5.2 

SSO 

83 

A.  P. 

15-3 

4.4 

457 

100 

Ham,  fresh,  lean     .     .    . 

E.  P. 

25.0 

14.4 

1042 

44 

A.  P. 

24.8 

14.2 

1030 

44 

fresh,  medium      .     .     . 

E.  P. 

iS-3 

28.9 

1458 

31 

A.  P. 

13-5 

25-9 

1303 

35 

smoked,  lean   .... 

E.  P. 

19.8 

20.8 

1209 

38 

A.  P. 

I7-S 

18.S 

1073 

42 

Herring,  whole    .... 

E.  P. 

19-5 

71 

644 

70 

A.  P. 

II. 2 

3-9 

362 

125 

*  Baker's  grade. 


326 


APPENDIX 
TABLE  I,  continued 


Food 


Herring,  smoked      .     .     .  E.  P. 
A.  P. 

Hominy 

Honey 

Huckleberries      .... 

Koumiss 

Lamb,  breast E.  P. 

A.  P. 

chops,  broiled  .     .     .     .  E.  P. 

fore  quarter     .     .     ,     .  E.  P. 

A.  P. 

hind  quarter    .     .     .     .  E.  P. 

A.  P. 

leg,  roast 

side E.  P. 

A.  P. 

Lard,  refined 

Lemon  juice 

Lemons E.  P. 

A.  P. 

Lettuce E.  P. 

A.  P. 

Liver,  beef E.  P. 

A.  P. 

veal E.  P. 

Lobster,  whole     .     .     .     .  E.  P. 
A.  P. 

canned A.  P. 

Macaroni 


Protein 
(Nx6.2s) 

PEE 
CENT 


36.9 
20.5 

8.3 

•4 

.6 

2.8 

19.1 

iS-4 
21.7 

18.3 
14.9 
19.6 
16.5 
19.7 
17.6 
14.1 


i.o 

•7 
1.2 
1.0 
20.4 
20.2 
19.0 
16.4 

5-9 
18.1 

134 


Fat 

PER 
CENT 


15.8 

8.8 
.6 

.6 
2.1 
23.6 
19.1 
29.9 
25.8 
21.0 
19.1 
16.1 
12.7 
23.1 
18.7 

lOO.O 

•7 
•5 
•3 
.2 

4-5 
3-1 
5-3 
1.8 

.7 
I.I 

•9 


Carbo- 
hy- 
drate 

PER 
CENT 


79.0 

81.2 

16.6 

5-4 


9.8 
8.5 
5-9 
2.9 

2-5 
1-7 

2-5 

.4 
.2 

•5 
74.1 


Fuel 
Value 
per 
Pound 
Calo- 
ries 


1315 

731 

1609 

1481 

336 

234 

1311 

1058 

1614 

138s 
1127 
1 149 

953 

876 

1263 

1015 

4086 

178 

201 

140 

87 

72 

583 
538 
562 

379 

139- 

382 

1625 


APPENDIX 
TABLE  I,  continued 


327 


Food 

Protein 

(NX6.25) 

PER 
CENT 

Fat 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 

cent 

Fuel 
Value 

PER 

Pound 
Calo- 
ries 

100 
Calorik 
Portion 
Grams 

Macaroons      .... 

. 

6.5 

15.2 

65.2 

1922 

24 

Mackerel 

.  E.  P. 

18.7 
10.2 

7-1 

4.2 

629 

3S6 

72 

A.  P. 

127 

salt 

.  E.  P. 

21. 1 

22.6 

1305 

35 

A.  P. 

16.3 

17.4 

IOCS 

45 

Marmalade,  orange .     . 

. 

.6 

.1 

84.S 

1548 

29 

Milk,  condensed,  sweetened 

8.8 

8.3 

54-1 

1480 

31 

skimmed      .... 

. 

34 

•3 

S.I 

167 

273 

whole 

. 

3-3 

4.0 

S-o 

314 

145 

Mincemeat,  commercial 

. 

6.7 

1.4 

60.2 

1280 

36 

homemade  .... 

. 

4.8 

6.7 

32.1 

942 

48 

Molasses,  cane     .     .     . 

2.4 

69.3 

1302 

35 

Mushrooms    .... 

.  A.  P. 

3-5 

•4 

6.8 

204 

223 

Muskmelons  .... 

.  E.  P. 

.6 

9-3 

180 

252 

A.  P. 

•3 

4.6 

89 

510 

Mutton,  fore  quarter    . 

.  E.  P. 

15.6 

30.9 

1543 

29 

A.  P. 

12.3 

24-5 

1223 

37 

hind  quarter    .     .    . 

.  E.  P. 

16.7 

28.1 

1450 

31 

A.  P. 

13.8 

23.2 

1197 

38 

W 

.  E.  P. 

19.8 
16.5 

12.4 

863 

52 

A.  P. 

10.3 

718 

63 

side 

.  A.  P. 

13-0 
16.2 

24.0 
29.8 

121S 
1512 

37 

E.  P. 

30 

Nectarines      .... 

.  E,  P. 

.6 
.6 

15-9 
14.8 

299 
280 

152 

A.  P. 

162 

Oatmeal 

. 

16.1 

7.2 

67.5 

1811 

25 

Okra 

.  E.  P. 

1.6 
1.4 

.2 
.2 

7-4 
6.5 

172 
152 

264 

A.  P. 

300 

Olives,  green  .... 

.  E.  P. 

I.I 

27.6 

11.6 

I3S7 

ZZ 

328 


APPENDIX 
TABLE  I,  continued 


Food 


Olives A.  P, 

ripe E.  P. 

A.  P, 

Onions,  fresh E.  P. 

A.  P. 

Oranges E.  P. 

A.  P. 
Oxtail  soup,  canned     .     .  A.  P. 

Oysters E.  P. 

in  shell A.  P. 

canned A.  P. 

Parsnips E.  P. 

A.  P. 
Pea  soup,  canned  ,  .  .A.  P. 
Peaches,  canned .     .     .     .  A.  P. 

fresh E.  P. 

A.  P. 

Peanuts E.  P. 

A.  P. 

Pears,  fresh E.  P, 

A.  P. 

Peas,  canned A.  P. 

dried 

green E.  P. 

A.  P. 

Pies,  apple 

custard 

lemon 

mince      


Pkotein 

(NX6.2S) 

PERCENT 


.8 

1-7 
1.4 
1.6 
1.4 
.8 
.6 
3-8 

6.2 
1.2 

8.8 

1.6 

1-3 

3-6 

•7 

•7 

•5 

25.8 

19-5 
.6 

•5 

3-6 

24.6 

7.0 

3-6 

3-1 
4.2 

3.6 


Fat 

PEK 
CENT 


20.2 
25.0 
21.0 

•3 
•3 
.2 
.1 

•5 

1.2 

.2 

2.4 

•5 

•4 

•7 

.1 

.1 

.1 

38.6 

29.1 

•5 

.4 

.2 

i.o 

•5 

.2 

9.8 

6.3 
10. 1 
12.3 


Carbo- 
hy- 
drate 

PER 
CEST 


8-5 
4-3 
3-5 
9.9 
8.9 
11.6 

8.5 
4.2 

3-7 
.7 

3-9 
13.5 
10.8 

7.6 
10.8 

9.4 

7-7 
24.4 

18.5 
14.1 
12.7 

9.8 
62.0 
16.9 

9.8 
42.8 
26,1 
37.4 
38.1 


Fuel 
Value  |     100 

PER     Calorie 
Pound   Portion 

Calo-     Grams 

RIES 


995 
1 130 

947 
220 
199 

233 
169 
166 
228 

43 
328 
294 
236 
232 
213 
188 

153 
2490 
1858 

288 

245 

252 

1611 

454 
252 

1233 

806 

1156 

1300 


APPENDIX 
TABLE  I,  continued 


329 


Food 


Pies,  squash 

Pineapples,  fresh     .     .     .  E.  P. 

canned A.  P. 

Pignolias E.  P. 

Pistachios,  shelled   .     .     . 

Plums E.  P. 

A.  P. 

Pomegranates     .     .     .     .  E.  P. 

Pork,  chops,  medium  .     .  E.  P. 

A.  P. 

chuck  ribs  and  shoulder  E.  P. 

A.  P. 

fat,  salt A.  P. 

sausage A.  P. 

side E.  P. 

A.  P. 

tenderloin A,  P. 

Potato  chips A.  P. 

Potatoes,  white,  raw    .     .  E.  P. 
A.  P. 

sweet,  raw E.  P. 

A.  P. 

Prunes,  dried E.  P. 

A.  P. 

Pumpkins E.  P. 

A.  P. 

Radishes E.  P. 

A.  P. 
Raisins E.  P. 


Protein 
(NX6.25) 

PERCENT 


4.4 
.4 
•4 

33-9 
22.3 

I.O 

•9 

1-5 

16.6 

13-4 

17.3 

14.1 

1.9 

13.0 

9.1 

8.0 

18.9 

6.8 

2.2 

1.8 

1.8 

1.4 

2.1 

1.8 

1.0 

.5 

1-3 

.9 

2.6 


Fat 

PER 
CENT 


8.4 

•3 

•7 
49.4 
54-0 


1.6 
30.1 
24.2 
3I-I 
2S-5 
86.2 
44.2 

55-3 
49.0 
13.0 

39-8 
.1 
.1 


.1 
.1 
,1 
.1 
3.3 


Carbo- 
hy- 
drate 

PER 

cent 


21.7 
9-7 
36.4 
6.9 
16.3 
20.1 
19.1 
19-5 


46.7 
18.4 
14.7 
27.4 
21.9 

73-3 
62.2 

5.2 
2.6 
5-8 
4.0 
76.1 


Fuel 
Value 

PER 

Pound 
Calo- 
ries 


100 
Calorie 
Portion 
Grams 


817 
196 

69s 

2748 

2900 

383 

363 

447 

1530 

1230 

1585 
1298 

3555 

2030 

2423 

2123 

875 

2598 

378 

302 

558 

447 

1368 

1 160 

117 

60 

133 

91 

1562 


56 
232 

65 

16 

16 

118 

125 

102 

30 

37 

29 

35 

13 

22 

19 

21 

52 

19 

120 

149 

81 

102 

33 

39 

389 

753 

341 

488 

29 


330 


APPENDIX 
TABLE  I,  continued 


Food 


Raisins A.  P. 

Raspberries,  red  .... 

black 

Rhubarb E.  P. 

A.  P. 

Rice 

Salmon,  dressed  .     .     .     .  A.  P. 

whole E.  P. 

A.  P. 

Sausage,  bologna.    .    .    .  E.  P. 

A.  P. 

farmer E.  P. 

A.  P. 

Shad,  whole E.  P. 

A.  P. 

roe 

Shredded  wheat  .... 
Spinach,  fresh      .     .     .     .  A.  P. 

Squash E.  P. 

A.  P. 

Strawberries 

Succotash,  canned    .     .     . 

Sugar 

Tomatoes,  fresh  .     .     .     ,  A.  P. 

canned A.  P. 

Turkey E.  P. 

A.  P. 
sandwich,  canned .     .     . 
Turnips E.  P. 


Protein 

Fat 

Carbo- 
hy- 

Fuel 
Valde 

100 

(NX6.25) 

PERCENT 

PER 
CENT 

drate 

PER 
CENT 

Pound 
Calo- 
ries 

Portion 
Grams 

2.3 

3-0 

68.5 

1407 

32 

I.O 

12.6 

247 

184 

1-7 

1.0 

12.6 

300 

151 

.6 

.7 

3-6 

los 

433 

•4 

.4 

2.2 

63 

714 

8.0 

•3 

79-0 

1620 

29 

13.8 

8.1 

582 

78 

22.0 

12.8 

923 

49 

15-3 

8.9 

642 

71 

18.7 

17.6 

•3 

1061 

43 

18.2 

19.7 

113s 

40 

29.0 

42.0 

2240 

20 

27.9 

40.4 

2156 

21 

18.8 

9-5 

727 

61 

9.4 

4.8 

367 

127 

20.9 

3-8 

2.6 

582 

78 

10.5 

1.4 

77.9 

1660 

27 

2.1 

•3 

3-2 

109 

417 

1.4 

•5 

9.0 

209 

217 

•7 

.2 

4.5 

103 

443 

1.0 

.6 

7-4 

169 

269 

3-6 

1.0 

18.6 

444 

102 

* 

lOO.O 

1815 

25 

•9 

•4 

3.9 

104 

438 

1.2 

.2 

4.0 

103 

443 

21. 1 

22.9 

1320 

34 

16.1 

18.4 

1042 

43 

20.7 

29.2 

1568 

29 

1-3 

.2 

8.1 

178 

256 

APPENDIX 
TABLE  I,  continued 


331 


Food 


Turnips A.  P. 

Veal,  breast E.  P. 

A.  P. 

cutlet E.  P. 

A.  P. 

fore  quarter     .     .     .     .  E.  P. 

A.  P. 

hind  quarter    .     .     .     .  E,  P. 

A.  P. 

side E.  P. 

A.  P. 
Vegetable  soup,  canned    . 
Walnuts,  California 


.  E.  P. 

A.  P. 
black E.  P. 

A.  P. 
Watermelons       .     .     .     .  E.  P. 

A.  P. 
Wheat,  cracked  .... 
Whitefish E.  P. 

A.  P. 
Zwiebach 


Protein 
{NX6.25) 

Fat 

PER 

Carbo- 
hy- 
drate 

Fuel 
Value 

PER 

Pound 
Calo- 
ries 

PER  CENT 

CENT 

PER 
CENT 

•9 

.1 

5-7 

124 

20.3 

II.O 



817 

15-3 

8.6 

629 

20.3 

7-7 

683 

20.1 

7.5 

670 

20.0 

8.0 

690 

I5-I 

6.0 

517 

20.7 

8.3 

715 

16.2 

6.6 

534 

20.2 

8.1 

697 

15.6 

6.3 

539 

2.9 

•5 

62 

18.4 

64.4 

13.0 

3182 

4.9 

17-3 

3-5 

859 

27.6 

56.3 

II. 7 

3001 

7.2 

14.6 

3-0 

780 

.4 

.2 

6.7 

136 

.2  • 

.1 

2.7 

57 

11^ 

1.7 

75-5 

1635 

/^'9 

6.5 

680 

/  10.6 

3-0 

315 

9.8 

9.9 

73-5 

1915 

100 
Calorie 
Portion 
Grams 


i 


36 
5 
72 
66 
68 
66 
88 
64 
85 
65 
84 

735 
14 
53 
15 
59 

332 

800 
28 
67 

144 
24 


332  APPENDIX 

TABLE  II 

Ash  Constituents  of  Foods  in  Percentage  of  the  Edible  Portion 
(Compiled  from  various  sources) 


Food 

CaO 

MgO 

K,0 

NazO 

P2O5 

CI 

s 

Fe 

Almonds      .     .     . 

•30 

•35 

.20 

•03 

.87 

•005 

•135 

.002 

Apples     .... 

.014 

.014 

•15 

.02 

•03 

.004 

.005 

.0003 

Apricots      .     .     . 

.018 

.018 

.28 

.06 

.06 

•003 

Asparagus   .     .     . 

.04 

.02 

.20 

.01 

.09 

.04 

.04 

.0010 

Bananas      .     .     . 

.01 

.04 

•50 

.02 

•055 

.20 

.013 

.0006 

Barley,  pearled     . 

.025 

.10 

•35 

.04 

.46 

.02 

.0013 

whole  .... 

.06 

.22 

•SO 

.06 

•95 

.02 

.14 

.004 

Beans,  dried    .     . 

.22 

.25 

1.40 

.26 

1. 14 

•03 

.22 

.0070 

lima,  dried    .     . 

.10 

•31 

2.1 

•33 

•77 

.025 

.16 

.0070 

lima,  fresh    .     . 

.04 

.11 

•7 

.12 

.27 

.009 

.06 

.0025 

string  .... 

•075 

•043 

.28 

•03 

.12 

.04 

.0016 

Beef  (see  Meat) 

Beer 

.007 

.010 

•059 

•059 

.089 

.014 

Beets 

.03 

•033 

•45 

.10 

.09 

.04 

.015 

.0006 

Blackberries     .     . 

.08 

•035 

.20 

.08 

.01 

Blueberries       .     . 

.045 

.015 

•05 

.02 

Bread,  white    .     . 

•03 

•03 

.10 

.20 

.12 

.0009 

whole  wheat     . 

.04 

.08 

.27 

•4 

.0015 

Breadfruit  .     .     . 

.12 

.01 

.28 

.04 

.16 

.10 

Buckwheat  flour  . 

.02 

.08 

.16 

.04 

.40 

.01 

Butter    .     .     .     . 

.02 

.001 

.02 

.03 

Buttermilk  .     .     . 

•IS 

.026 

.18 

.08 

.22 

.10 

Cabbage      .     .     . 

.068 

.026 

•45 

•05 

.09 

•03 

.07 

.0011 

Cocoa     .     .     .     . 

.14 

.48 

I.O 

•05 

I.I 

.04 

.0024 

Capers    .     .     .     . 

.17 

.04 

•25 

.07 

.14 

•27 

Caraway  seed  .     . 

•9 

•4 

^•3 

•3 

1.2 

•15 

Carrots   .     .     .     . 

.077 

.034 

•35 

•13 

.10 

.036 

.022 

.0008 

Cauliflower .     .     . 

•17 

.02 

.27 

.10 

.14 

•05 

.085 

Caviar     .     .     .     . 

.19 

•13 

1.2 

•4 

1.8 

APPENDIX 
TABLE  II,  continued 


'    333 


Food 

CaO 

MgO 

K2O 

NajO 

P205 

CI 

S 

Fe 

Celery     .... 

.10 

.04 

•37 

.11 

.10 

•17 

•02s 

.0005 

Cheese,  hard    .     . 

I.I 

.06 

.2 

I. 

i^4S 

I. 

Cottage  cheese     . 

•3 

.CIS 

•S 

Cherries .... 

•03 

.027 

.26 

.03 

,07 

.01 

.0005 

Cherry  juice     .     . 

.025 

.02 

•IS 

.02 

•03 

.004 

.006 

Chestnuts    ,     .     . 

.04 

.08 

•SO 

•OS 

.20 

.01 

.068 

.001 

Chicory  .... 

•OS 

•03 

.27 

.11 

.00 

.06 

Chives     .... 

.20 

•OS 

■ZZ 

.04 

.20 

.04 

Chocolate    .     .     . 

.14 

.48 

.90 

Citron     .... 

.17 

•03 

•2S 

.02 

.08 

.01 

Cocoanut  pulp 

.09 

.10 

•77 

.10 

•38 

•25 

Codfish  {see  Fish) 

Coffee 

•25 

.42 

2-3 

.08 

•OS4 

.04 

Corn,  sweet,  dried 

•03 

.20 

•5 

.2 

.8 

•OS 

.16 

.0029 

sweet,  fresh  .     . 

.008 

•OSS 

•137 

•OS 

.22 

.014 

.044 

.0008 

Corn  meal  .     .     . 

.015 

•13 

•17 

•03 

•3 

.116 

.0011 

Crackers,  soda      . 

.028 

.017 

.12 

•23 

.12 

.001  s 

Cranberries      .     . 

.024 

.011 

.09 

.013 

•03 

.008 

.0006 

Cream     .... 

.14 

.02 

•IS 

.06 

.18 

.1 

•03 

.0002 

Cucumbers .     .     . 

.022 

.015 

•17 

.CIS 

.08 

•03 

.022 

Currants,  fresh     . 

•OS 

.04 

•2S 

.02 

,10 

.01 

.01 

.coos 

Zante  .... 

.14 

.08 

I.O 

.1 

•3 

.06 

Currant  juice  .     . 

•03 

.02 

.2 

•05 

Dandelion  greens 

.0027 

Dates      .... 

.10 

.12 

•003 

Eggs 

•093 

.015 

.i6s 

.2 

•37 

.10 

.19 

.003 

Egg  white    .     .     . 

.015 

•ois 

.19 

.21 

•03 

•IS 

.196 

.0001 

Egg  yolk     .     .     . 

.2 

.02 

•13 

.1 

1.0 

.1 

•IS7 

.008s 

Endive    .... 

.14 

.02 

•45 

•IS 

.10 

.03 

Figs,  fresh  .     .     . 

.074 

.036 

.365 

.016 

.082 

.014 

.0008 

dried   .... 

.299 

.145 

1.478 

.064 

.332 

.os6 

.0032 

Fish,icod    .     .     . 

.015 

•03 

.40 

•13 

.4 

.24 

.0004 

1  Average  fish  flesh  is  calculated  to  contain  per  100  grams  protein  .15 
CaO,  .2  MgO,  2.5  P2O5,  .004  Fe. 


334 


APPENDIX 
TABLE  II,  continued 


Food 

CaO 

MgO 

K/) 

Na^ 

P,05 

CI 

S 

Fe 

haddock  .     .     . 

•03 

.04 

.40 

•13 

•4 

.24 

.22 

halibut     .     .     . 

.013 

•4 

.CX303 

herring     .     .     . 

.08 

•05 

•55 

•23 

herring  roe   .     . 

.012 

.06 

pike     .... 

•05 

•OS 

•4 

•15 

.48 

04 

.22 

salmon     .     .     . 

.011 

•05 

•32 

•17 

.42 

.28 

.0015 

Flaxseed      .     .     . 

.27 

.42 

1.04 

.06 

1.30 

.17 

Flour    {see   under 

wheat,       buck- 

wheat,  etc.) 

Gooseberries    .     . 

•05 

.02 

.21 

•03 

.65 

.01 

Grapefruit  ,     .     . 

•03 

.02 

.17 

.04 

.01 

.0004 

Grapes    .... 

.024 

.014 

•25 

•03 

.12 

.01 

.024 

.0013 

Grape  juice    (and 

must)  .... 

.021 

.016 

.20 

.01 

.04 

.01 

Guava    .... 

.02 

.013 

.46 

.07 

.05 

Haddock  (see  Fish) 

Halibut  {see  Fish) 

Hazelnuts   .     .     . 

.004 

Honey    .... 

.005 

•03 

•5 

.04 

•03 

.0010 

Horseradish  •    .     . 

•13 

.065 

.56 

.08 

.1 

.02 

.18 

Huckleberries  .     . 

•035 

.025 

.07 

.0011 

Infants'  foods  ^     . 

Lamb  {see  Meats) 

Leeks      .... 

.08 

.02 

.24 

.11 

•15 

.03 

.08 

Lemons  .... 

•05 

.01 

.21 

.01 

.02 

.01 

.012 

.0006 

Lemon  juice     .     . 

•033 

.01 

.17 

.01 

.025 

.01 

Lemon,  sweet  .     . 

.04 

.01 

.53 

.10 

.01 

Lentils    .... 

.12 

•05 

.75 

.25 

.66 

.08 

.0086 

Lettuce  .... 

•05 

.01 

.42 

.04 

.09 

.06 

.014 

.001 

1  Ash  analyses,  more  or  less  complete,  of  a  number  of  proprietary  foods 
are  given  in  Konig's  Cliemie  der  Nahrungs-  tend  GeniissmiUel,  4th  ed. 


APPENDIX 
TABLE  n,  continued 


335 


Food 

CaO 

MgO 

K2O 

NajO 

PA 

CI 

s 

Fe 

Limes     .... 

.08 

.02 

.42 

.08 

.04 

Mamey  .... 

.02 

.02 

.42 

.06 

.14 

Mango    .... 

•03 

.01 

.28 

.04 

.02 

Maple  sap  .     .     . 

•17 

.06 

.25 

.01 

.06 

Meat/  beef,  lean  . 

.Oil 

.04 

.42 

.09 

•50 

•05 

.20 

.0038 

veal,  lean      .     . 

.016 

•045 

.46 

.12 

•50 

•07 

.23 

ox  tongue     .     , 

.028 

.02 

•56 

.06 

.60 

chicken    .     .     . 

.015 

.06 

•56 

•13 

•58 

.06 

.216 

pork,  lean     .     . 

.012 

.046 

•34 

•13 

•45 

•05 

.20 

ham    .... 

.032 

.04 

rabbit's  flesh     . 

.026 

•05 

.48 

.07 

.58 

•05 

.20 

frog's  flesh    .     . 

.027 

.04 

•37 

.07 

.43 

.04 

.16 

Meat  extracts  2 

Meat  sauces'^ 

Milk,  cow's      .     . 

.168 

.019 

.171 

.068 

.215 

.12 

•033 

.00024 

Molasses     .     .     . 

•9 

•3 

1^7 

•3 

.2 

.2 

Mushrooms      .     . 

.024 

.026 

.46 

.04 

.24 

.02 

•03 

Muskmelons     .     . 

.024 

.020 

.283 

.082 

•035 

.041 

.014 

.0003 

Mustard      .     .     . 

.689 

•430 

.917 

.076 

1.729 

.016 

1.230 

Mutton  {see  Meat) 

Oatmeal  .... 

.13 

.212 

.458 

.109 

.872 

•035 

.215 

.0036 

Olives      .... 

.17 

.01 

1.8 

.17 

•03 

.01 

.0029 

Onions     .... 

.06 

•03 

•23 

.02 

.12 

.02 

.06 

.0005 

Oranges  .... 

.06 

.02 

.22 

.01 

•05 

.01 

.013 

.0003 

Orange  juice     .     . 

•05 

.02 

,22 

.01 

.03 

.01 

Paprika  .... 

•32 

.27 

2.5 

.24 

•78 

•IS 

Parsnips       .     .     . 

.09 

.07 

.70 

.01 

.19 

•03 

Peaches  .... 

.01 

.02 

.25 

.02 

.047 

.01 

.01 

.0003 

*  Average  meat  is  calculated  to  contain  per  100  grams  protein  .075  CaO, 
.2  MgO,  2.0  KoO,  .4  Na20,  2.3  P2O5,  .2  CI,  .9  S,  .015  Fe. 

2  See  Konig's  Chemie  der  menschlichen  Nahrungs-  und  Geniissmittel, 
4th  ed. 


33<5 


APPENDIX 
TABLE  II,  continued 


Food 

CaO 

MgO 

K,0 

Na,0 

P2O5 

CI 

s 

Fe 

Peanuts  .... 

.10 

.28 

.85 

.07 

.90 

.04 

•243 

.0020 

Pears       .... 

.021 

.019 

.16 

.03 

.06 

.0003 

Peas,  dried  .     .     . 

.14 

.24 

1.06 

.16 

.91 

.04 

•23 

.0056 

fresh  (calc.  from 

dried)  •     ..    •     • 

.04 

.07 

•30 

.04 

.26 

.01 

.06 

.0016 

cow  peas,  dried . 

.18 

.21 

1 .01 

.40 

I. GO 

.02 

Persimmons      .     . 

.03 

.015 

•35 

.02 

•05 

.01 

Pie,  mince    .     .     . 

.04 

.04 

.2 

squash      .     .     . 

•03 

.02 

•IS 

Pineapple     .     .     . 

.02 

.02 

.38 

.02 

.06 

•05 

.0005 

juice     .... 

.02 

•05 

.007 

Plums      .... 

.025 

.02 

•25 

•03 

•055 

.01 

.0005 

Pork  {see  Meat) 

Potatoes       .     .     . 

.016 

.036 

.53 

.025 

.140 

•03 

•03 

.0013 

sweet   .... 

.025 

.02 

.47 

.06 

.09 

.12 

.0005 

Prunes,  dried    .     . 

.06 

.08 

1.2 

.1 

•25 

.01 

•03 

.0029 

Pumpkins    .     .     . 

•03 

.015 

.08 

.08 

.11 

.01 

.02 

Quince  juice     .     . 

.18 

•035 

Radishes      .     .     . 

.05 

.02 

.17 

.11 

.09 

•05 

•05 

.0006 

Raisins    .... 

.08 

•15 

I.O 

.19 

.29 

.07 

.06 

.005 

Raspberries       .     . 

.07 

.04 

.21 

.12 

Raspberry  juice    . 

•03 

•03 

•17 

.01 

•03 

.01 

.007 

Rhubarb      .     .     . 

.06 

.02 

•39 

•03 

.07 

•035 

Rice 

.012 

•045 

.084 

.028 

.203 

•05 

•  lOS 

.0009 

Rutabagas    .     .     . 

.1 

•03 

.48 

.11 

.13 

Rye 

.07 

.22 

.60 

.04 

.81 

.02 

•17 

.004 

Rye  flour     .     .     . 

.018 

•13 

.60 

•03 

:8o 

Rye  bran      .     .     . 

•25 

l.l 

1.9 

.1 

3-4 

Salsify     .     .     .     . 

.12 

.04 

Sapato     .... 

.04 

.02 

.22 

.02 

.09 

.01 

Soup,  canned  vege- 

table   .     .     .     . 

.025 

.02 

.18 

.11 

Spinach  .     .     .     . 

.09 

.08 

.94 

.20 

•13 

.02 

.041 

.0032 

APPENDIX 
TABLE  II,  continued 


337 


Food 

CaO 

MgO 

K20 

NaaO 

P2O5 

CI 

S 

Fe 

Squash    .... 

.02 

.01 

.05 

.05 

.08 

.01 

.026 

.0008 

Strawberries     .     . 

•OS 

•03 

.18 

.07 

.064 

.01 

.0009 

Tamarinds  .     .     . 

.01 

•03 

.15 

.01 

.01 

Tomatoes     .     .     . 

.020 

.017 

•3S 

.01 

.059 

•03 

.02 

.0004 

Tomato  juice    .     . 

.01 

.017 

■ZS 

.02 

•034 

•05 

Turnips  .... 

.089 

.028 

.40 

.08 

.117 

.04 

.07 

.0005 

Turnip  tops      .     . 

.48 

•OS 

.37 

.11 

.11 

.17 

•07 

Vanilla  (bean)  .     . 

I.O 

•5 

.85 

.35 

.6 

.03 

Veal  {see  Meat) 

Vinegar   .... 

.02 

.02 

.25 

•OS 

Walnuts  .... 

.108 

.237 

.44 

•03 

•77 

.01 

.195 

.0021 

Water  chestnuts    . 

.12 

■2S 

.77 

•03 

•79 

.01 

Water  cress       .     . 

.26 

•OS 

•07 

Watermelon      .     . 

.02 

.02 

•09 

.01 

.02 

.01 

Wheat,  entire  grain 

.061 

.213 

.519 

.068 

.902 

.08 

.17 

•0053 

Wheat  flour      .     . 

.025 

.027 

.146 

.04 

.20 

.07 

.17 

.0015 

low  grade      .     . 

.04 

•07 

.23 

•37 

Wheat  bran      .     . 

.14 

.84 

i.S 

.07 

3^o 

.26 

Whortleberries      . 

.037 

.024 

.21 

.03 

.06 

Wine 

.012 

.019 

.100 

.018 

.036 

.01 

338 


APPENDIX 


TABLE  in 

Ash  Constituents  of  Foods  est  Grams  per  ioo  Calories  of  Edible 
Food  Material 

(Estimated  from  preceding  tables) 


Food 

CaO 

MgO 

K,0 

NajO 

PiOg 

CI 

S 

Fe 

Almonds      .     .     . 

.046 

•053 

.030 

.004 

.132 

.001 

.020 

.0003 

Apples     .... 

.022 

.022 

.237 

•03 

•05 

.006 

.008 

.0005 

Apricots  .... 

.031 

.031 

.485 

.10 

.10 

.005 

.01 

Asparagus   .     .     . 

•17 

.09 

.88 

.04 

.39 

•17 

.17 

•0043 

Bananas  .... 

.01 

.04 

•50 

.02 

•055 

.20 

.013 

,0006 

Bariey  flour,  patent 

•083 

.031 

.00028 

Barley,  pearled     . 

.007 

.028 

.097 

.Oil 

.127 

•005 

.00036 

Beans,  dried     .     . 

•063 

.072 

.401 

.074 

.326 

.008 

.063 

.0020 

lima     .... 

.028 

.087 

•59 

.092 

.219 

.007 

•045 

.00195 

string  .... 

.177 

.102 

.663 

.070 

.284 

.10 

.0038 

Beets       .... 

.06 

.071 

•965 

.21 

.19 

.08 

•032 

.0013 

Blackberries     .     . 
Blueberries       .     . 

•13 

.060 

•059 
.020 

■33 
.07 

•13 
•03 

.02 

Bread,  white    .     . 

.011 

.Oil 

.04 

.075 

•05 

.0003 

"whole  wheat" 

.016 

.032 

.109 

.16 

.0006 

graham    .     .     . 

.019 

.19 

.0013 

Buckwheat  flour  . 

.006 

.022 

•045 

.oil 

.114 

.003 

Butter    .... 

.003 

.0001 

•003 

.004 

Buttermilk .     .     . 

•415 

.072 

•495 

.22 

.61 

•275 

Cabbage      .     .     . 

.214 

.081 

1.425 

.16 

.28 

.09 

.22 

•0035 

Cacao  (cocoa)  ^     . 

.027 

•095 

.20 

.010 

.22 

.008 

.0005 

Carrots  .... 

.168 

.074 

.765 

.28 

.22 

.078 

.048 

.0016 

Cauliflower .     .     . 

.55 

.06 

.88 

•32 

.45 

.16 

•277 

Celery     .... 

.54 

.22 

2.00 

.60 

•54 

•9 

•13 

.0027 

Cheese,  hard    .     . 

.25 

.014 

.05 

.2 

•329 

.2 

Cottage  cheese     . 

•3 

.013 

•4 

Cherries  .... 

.04 

•034 

.32 

.04 

.09 

.01 

General  average  of  samples  of  beans,  nibs,  and  powdered  sample. 


APPENDIX 
TABLE  III,  continued 


339 


Food 

CaO 

MgO 

K2O 

NazO 

P2O5 

CI 

S 

Fe 

Chestnuts    .     .     . 

.017 

•034 

.21 

.02 

.08 

.004 

.028 

.0004 

Chocolate    . 

. 

.02 

.08 

.14 

Citron     .     . 

. 

.052 

.009 

.076 

.006 

.024 

.003 

Coconut  pulp 

. 

•015 

.016 

.129 

.Oil 

.063 

.042 

Corn,  green 

.008 

•053 

.134 

•05 

.21 

.014 

.042 

.00075 

Corn  meal   . 

.004 

.036 

•05 

.01 

.08 

•032 

.0003 

Crackers,  soda 

.006 

.004 

.028 

•054 

.028 

.00035 

Cranberries 

.051 

.023 

.19 

.027 

.06 

.017 

.0013 

Cream     .     . 

.07 

.01 

.07 

•03 

.10 

•05 

.01 

.0001 

Cucumbers . 

.12 

.09 

I.O 

.09 

•45 

.2 

.12 

Currants,  fresh 

.09 

.07 

•43 

•03 

•17 

.02 

.02 

.0009 

Zante  .     . 

.04 

.02 

•3 

•03 

.09 

.02 

Dates     .     . 

.03 

•03 

.001 

Eggs  .     .     . 

.06 

.009 

.108 

.1 

.24 

.06 

.12 

.0019 

Egg  white   . 

.028 

.028 

•355 

•395 

•05 

.28 

•370 

.0002 

Egg  yolk     . 

•05 

.005 

•035 

•03 

.27 

•03 

•043 

.0023 

Figs    .     .     . 

.089 

•043 

.442 

.019 

.099 

.017 

.0010 

Fish,  cod     . 

.021 

.04 

•57 

.18 

.6 

•34 

.0006 

haddock  . 

.04 

•OS 

•55 

.18 

•5 

•33 

•30 

halibut     . 

.010 

•3 

.0002 

herring    . 

•05 

•03 

•38 

.16 

pike     .     . 

.06 

.06 

•5 

.19 

.60 

•05 

.27 

salmon     . 

.005 

.02 

•15 

.08 

.20 

.13 

.0007 

Grapes    .     . 

.024 

.014 

•25 

•03 

.12 

.01 

.024 

.0013 

Grape    juice 

md 

must  .     . 

.021 

.016 

.20 

.01 

.04 

.01 

Honey    .     . 

.001 

.01 

•13 

.01 

.01 

.0003 

Horseradish 

.26 

.129 

.III 

.16 

.2 

.04 

•35 

Huckleberries 

.046 

.033 

.09 

.0014 

Leeks     .     .     . 

.24 

.06 

•73 

-3,3 

•45 

.09 

.24 

Lemons  .     . 

.12 

.02 

.46 

.02 

.04 

.02 

.027 

.0013 

Lemon  juice 

.083 

•03 

•43 

•03 

.063 

•03 

Lentils    .     . 

•03 

,01 

.21 

.07 

.18 

.02 

.0024 

340 


APPENDIX 
TABLE  III,  continued 


Food 

CaO 

MgO 

K^ 

NajO 

P2O5 

CI 

S 

Fe 

Lettuce  .... 

.26 

•05 

2.1 

.2 

.47 

•3 

.07 

.005 

Maple  sap  . 

.06 

.02 

.09 

.003 

.02 

Meats,  bacon 

. 

.001 

•003 

.04 

.0002 

beef,  lean 

.     . 

.009 

•03 

•35 

.08 

.42 

.04 

•17 

.0032 

veal,  lean 

. 

.012 

•033 

•34 

.09 

•37 

•05 

•17 

chicken    . 

.     . 

.007 

.03 

.24 

.06 

•25 

.02 

.08 

ham    . 

.     . 

.005 

.014 

.18 

.0011 

frog's  flesh 

.     . 

.042 

.06 

•57 

.11 

•67 

.06 

•25 

Milk,  cow's 

. 

•239 

.027 

•243 

.097 

•303 

•17 

•047 

.00034 

Molasses      . 

. 

•3 

.1 

.6 

.1 

.1 

.1 

Mushrooms 

. 

•053 

.057 

I.OI 

.09 

.53 

.04 

.06 

Oatmeal 

. 

•03 

.052 

•113 

.027 

.216 

.009 

.053 

.0009 

Olives     .    . 

. 

.06 

.003 

.6 

.06 

.01 

.003 

.0009 

Onions    .     . 

. 

.12 

.06 

.46 

.04 

.24 

.04 

.12 

•OOII 

Oranges  .    . 

. 

.11 

.04 

.42 

.02 

.09 

.02 

.025 

.0006 

Orange  juice 

. 

.12 

•OS 

•51 

.02 

.07 

.02 

Parsnips      .     . 

. 

.14 

.11 

1.07 

.02 

.29 

•05 

Peaches  .     .     . 

. 

.02 

•05 

.60 

•05 

•113 

.02 

.02 

.0007 

Peanuts       .     . 

. 

.018 

.049 

.152 

.012 

.160 

.007 

.043 

.00035 

Pears      .     .    . 

. 

.032 

.029 

•25 

•05 

.09 

.0005 

Peas,  dried 

. 

.04 

.07 

.29 

.04 

•25 

.01 

.06 

.0015 

fresh   .     .     . 

. 

.032 

.054 

.29 

.01 

.24 

.01 

.06 

.0016 

Cowpeas      .     . 

. 

•05 

.06 

•29 

.11 

.29 

.006 

Persimmons     . 

. 

.02 

.011 

.25 

.01 

.04 

•01 

Pie,  mince  .     . 

, 

.01 

.01 

.1 

squash     .     . 

.02 

.01 

.08 

Pineapple    .     . 

. 

.04 

.04 

.87 

.04 

•  14 

.11 

.0011 

Plums     .     .     . 

. 

.029 

.02 

.029 

•03 

.064 

.01 

.0006 

Potatoes      .     . 

• 

.019 

.042 

.63 

.030 

.166 

.04 

.04 

.0015 

sweet  .     .     . 

. 

.020 

.02 

•37 

.05 

.08 

.10 

.0004 

Prunes,  dried  . 

. 

.02 

•03 

•4 

.03 

.08 

.003 

.01 

.0009 

Pumpkins   .     . 

. 

.11 

•057 

•30 

•30 

.42 

.038 

.08 

Radishes      .     . 

• 

•17 

.07 

•57 

•37 

•30 

•17 

•17 

.0020 

APPENDIX 
TABLE  III,  continued 


341 


Food 

CaO 

MgO 

K,0 

NaaO 

P2O6 

CI 

S 

Fe 

Raisins  .     .    .     . 

.02 

.04 

•3 

.05 

.08. 

.02 

.02 

.001 

Raspberries      .     . 

.11 

.06 

•335 

.18 

Raspberry  juice    . 

.08 

.08 

•45 

.03 

.08 

•03 

.019 

Rhubarb      .     .     . 

.26 

.09 

1.69 

.13 

•30 

•151 

Rice 

.003 

.013 

.023 

.008 

•057 

.01 

.029 

.0003 

Rutabagas  .     .     . 

.2 

.07 

1. 16 

.26 

•31 

Rye  flour     .     .     . 

.005 

.04 

•17 

.01 

.22 

Soup  (canned  veg- 

etable)    .     .     . 

.18 

•15 

1^3 

.8 

Spinach  .     .     .     . 

•37 

•33 

3.905 

•83 

•54 

.08 

.170 

•0133 

Squash    .     .     .     . 

.04 

.02 

.11 

.11 

•17 

.02 

.055 

.0017 

Strawberries     .     . 

•13 

.08 

.45 

.18 

.162 

.03 

.0023 

Tomatoes    .     .     . 

.087 

.074 

1.52 

.04 

•257 

•13 

.09 

.0017 

Turnips  .     .     .     . 

.222 

.070 

1. 00 

.20 

.292 

.10 

.17 

.0013 

Turnip  tops      .     . 

1. 00 

.10 

•77 

•23 

.23 

•35 

.14 

Walnuts       .     .     . 

.015 

•033 

.061 

.004 

.108 

.001 

.027 

.00029 

Watermelon     .     . 

.06 

.06 

.29 

•03 

.06 

•03 

Wheat  flour      .     . 

.007 

.007 

.040 

.01 

•05 

.02 

•05 

.0004 

low  grade     .     . 

.01 

.02 

.006 

.10 

Whortleberries 

.043 

.028 

.24 

•03 

•07 

.02 

INDEX 


Abderhalden,  on  action  of  inorganic 
iron,  242 ;  on  digestion  products  of 
protein,  102,  104;  on  hydrolysis  of 
casein,  39 ;  of  globulin,  392 ;  on  rate 
of  growth,  273 ;  on  relation  of  pep- 
tids  to  peptones,  34. 

Acetonitrile,  effect  of  diet  on  resistance 
to,  313- 

Acid,  aspartic,  37,  39,  301 ;  butyric,  17 ; 
capric,  18;  caproic,  17;  caprylic,  17; 
erucic,  19;  glutamic,  37,  39,  301; 
lauric,  19;  linoleic,  20;  linolenic,  20 ; 
myristic,  18;  oleic,  19;  palmitic,  18; 
phycetoleic,  19;  stearic,  18. 

Acid-forming  diet,  292. 

Acid-forming  elements  in  food  ma- 
terials, 292,  295. 

Acidity  of  fruits,  296. 

Acids,  fatty,  17. 

Activating  substances,  50. 

Adenase,  53,  114. 

Age,  influence  on  food  requirement, 
168;  on  protein  requirement,  201. 

Alanin,  amounts  from  proteins,  39, 
301 ;  formation  of  glucose  from,  108 ; 
structure,  36. 

Albu  and  Neuberg,  pn  calcium  require- 
ment, 289. 

Albuminoids,  27,  31. 

Albumins,  26,  30. 

Albumoses,  see  Proteoses. 

Alcohol-soluble  proteins,  27,  30. 

Almonds,  43,  129,  282,  288,  315,  332, 
338. 

Amandin,  301. 

Amino  acids,  36;  amounts  from  pro- 
teins, 39,  301 ;  anhydrides  of,  23 ; 
cleavage  of,  iii;  diamino  acids, 
37  ;  food  value,  302 ;  in  metabolism, 
references,  116;  in  proteins,  39,  301  ; 
heterocyclic,  38 ;  structure,  37 ; 
thio-amino  acids,  38. 


Ammonia,  amounts  from  proteins,  39, 
301;  ehmination  of,  112;  in  protein 
metaboHsm,  iii,  112. 

Amylolytic  enzymes,  47,  85. 

Amylopsin,  84,  53,  49. 

Animal  fat,  composition,  20. 

Appetite,  218. 

Apples,  43,  129,  251,  282,  288,  295,  319, 
332,338;  evaporated,  315. 

Apricots,  319,  332,  338. 

Arginin,  amounts  from  proteins,  30, 
301 ;  from  protein  metabolism,  in  ; 
structure,  37. 

Armsby,  on  energy  metabolism,  147, 
149,  175;  on  fate  of  foodstuffs, 
116. 

Artificial  digestion  experiments,  304. 

Ash  constituents  of  foods,  260,  267, 
282,  290,  291,  295,  332,  336;  table 
of,  in  loo-calorie  portions,  338;  in 
percentage  of  edible  portion,  332. 

Ash-free  diet,  292. 

Asparagus,  43,  128,  319,  3*32,  338. 

Aspartic  acid,  amounts  from  proteins, 
39,  301;  structure,  37. 

Atwater,  on  bomb  calorimeter,  119; 
on  coefficients  of  digestibility  of 
food,  76 ;  on  food  requirements,  144, 
155.  1Q9;  on  muscular  work  and 
metabolism  of  protein,  199;  on 
protein-sparing  power  of  fat  and 
carbohydrates,  191 ;  on  respiration 
calorimeter,  142. 

Atwater  and  Benedict,  on  heat  produc- 
tion in  fasting,  150;  on  metabolism 
under  different  conditions  of  activ- 
ity, 161. 

Atwater's  dietary  standards,  206, 
207. 

Atwater-Rosa-Benedict  respiration  cal- 
orimeter, 142. 

Autolytic  enzymes,  53,  104. 


343 


344 


INDEX 


Bacon,  43,  128,  295,  315,  319,  340. 

Bacterial  action  in  digestive  tract,  78, 
79,  80. 

Balance  of  acid-  and  base-forming 
elements  in  foods,  294. 

Bananas,  43,  129,  282,  288,  319,  332, 
338. 

Barley,  319,  332,  338. 

Barley  flour,  251. 

Base-forming  elements  in  food  ma- 
terials, 295. 

Basel  Insurance  Company  on  relation 
of  weight  to  height,  214. 

Bayliss  and  Starling,  on  hormone, 
secretin,  67. 

Beans,  43,  128,  295;  baked,  canned, 
320;  dried,  315,  319,  332,  338; 
Lima,  canned,  320,  338 ;  Lima,  dried, 
251.  319,  332 ;  Lima,  fresh,  320,  332 ; 
navy,  dried,  251,  282,  288;  string, 
251,  320,  332,  338;  string,  canned, 
320. 

Beaumont's  observations  on  the  stom- 
ach, 56. 

Beef,  43,  128,  282,  295,  301,  335,  340; 
composition  of  diflferent  cuts,  320- 
323  ;  digestibility  when  cooked  in  dif- 
ferent ways,  305. 

Beets,  43,  128,  282,  288,  322,  332,  338. 

Benedict,  on  protein  in  diet,  226;  on 
protein  metabolism  in  fasting,  180. 

Benedict  and  Carpenter,  calorimeter 
experiments,  146. 

Benedict  and  Osterberg,  on  composition 
of  human  fat,  22. 

Berthelot  bomb  calorimeter,  119. 

BUe,  66,  68. 

Blackberries,  322,  332,  338. 

Blackfish,  322. 

Blood,  glucose  content  of,  7,  86. 

Blueberries,  332. 

Bluefish,  322. 

Body  fat,  relation  to  food  requirement, 
213. 

Body,  human,  elementary  composition 
of,  260 ;  size  and  shape,  influence  on 
metaboUsm,  165 ;   surface,  167. 

Bomb  calorimeter,  119. 

Boston  crackers,  322. 

Brazil  nuts,  322. 


Bread,  128,  315;  graham,  322,  338; 
milk,  322;  rolls,  water,  322;  toasted, 
322;  Vienna,  322;  white  home- 
made, 43,  322,  332,  338;  white  and 
brown,  iron  in,  256;  whole  wheat, 
322,  332,  338. 

Bread-fruit,  332. 

Breadstuffs,  coefficients  of  digestibility, 
76. 

British  gum,  preparation  of,  14. 

Browne,  on  composition  of  butter  fat, 
23- 

Buchner,  on  alcoholic  fermentation,  44. 

Buckwheat  flour,  322,  332,  338. 

Bunge,  on  craving  for  salt,  263;  on 
iron  in  foods,  233 ;  on  loss  of  Ume  in 
pregnancy,  288;  on  rate  of  growth, 
273. 

Butter,  43,  128,  315,  322,  332,  338. 

Butter  fat,  23. 

Buttermilk,  322,  332,  338. 

Butternuts,  322. 

Butyric  add,  17. 

Cabbage,  43,  128,  251,  295,  323,  332, 
338. 

Calcium,  amount  in  body,  261 ;  bal- 
ance in  study  of  food  values,  312; 
efi'ect  of  insufficient,  286;  functions 
in  body,  283  ;  in  children's  diet,  288 ;  1 
in  food  and  nutrition,  286;  in  food 
materials,  table,  290;  in  milk  of 
different  species,  274;  requirement, 
287,  289;  calcium  rigor,  284;  elimi- 
nation of,  286. 

Calf's-foot  jelly,  323. 

Calories,  requirement  per  day,  132. 

Calorific  value,  see  Combustion. 

Calorimeter,  bomb,  119;  experiments, 
144,  142,  145;  references,  147; 
respiration,  142. 

Camerer,  on  influence  of  age  on  metab- 
oUsm, 169. 

Cane  sugar,  see  Sucrose. 

Cannon,  on  movements  of  the  stomach, 
56 ;  rate  of  passage  of  different  foods 
through  the  digestive  tracts,  71; 
stomach  movements  in  digestion,  61. 

Caj)ers,  332. 

Capric  acid,  18. 


INDEX 


345 


Caproic  acid,  17. 

Caprylic  acid,  17. 

Carbohydrates,  3,  4;  conversion  into 
fat,  90 ;  digestion  of,  84 ;  fate  of  in 
metabolism,  86 ;  formation  from 
protein,  106;  formation  from  fat, 
98;  heat  of  combustion,  122,  123; 
hydrolysis  by  enzymes,  52 ;  metab- 
olism of,  references,  116;  protein- 
sparing  power,  185;  references,  40; 
respiratory  quotient,  88;  storage  in 
liver,  86 ;  synthesis  of,  in  plants,  4. 

Carbon  balance,  140,  309. 

Carrots,  43,  128,  282,  288,  323,  332, 
338. 

Casein,  301 ;  amino  acids,  39 ;  as 
source  of  phosphorus,  272  ;  ultimate 
composition,  35. 

Catalyzers,  enzymes  as,  45. 

CauUflower,  323,  332,  338. 

Caviar,  332. 

Celery,  43,  128,  295,  323,  333,  338; 
soup,  canned,  323. 

Cellulose,  utilization,  311. 

Cereals,  coefficients  of  digestibility,  76. 

Cetti  and  Breithaupt,  iron  require- 
ment of,  247. 

Cheese,  323,  333,  338. 

Chemical  composition  of  foods,  41,  43, 
298,  319,  332,  338. 

Cherries,  323,  333,  338. 

Chestnuts,  43,  129,  323,  333,  339. 

Chicken,  301,  323,  335,  340. 

Chicory,  333. 

Children,  food  requirements,  171 ;  iron 
requirement,  248 ;  need  for  calcium, 
288;   protein  requirement,  201. 

Children's  diet,  kind  of  protein  re- 
quired, 202. 

Chittenden,  dietary  standards,  210; 
on  peptones,  34 ;  on  protein  in  diet, 
222,  227;  on  protein  requirement, 
193 ;  on  protein  synthesis  by  auto- 
lytic  enzymes,  104. 

Chives,  333. 

Chlorides,  metabolism  of,  262. 

Chlorine,  excretion  per  day  on  salt- 
free  diet,  264. 

Chocolate,  323,  333,  339. 

Chyme,  passage  of  into  intestine,  64. 


Circulation,  work  of,  149. 

Citron,  333,  339. 

Coagulated  proteins,  28. 

Cocoa,  324,  332,  338. 

Coconut  pulp,  333,  339. 

Cod,  43,  128,  333,  339;  dressed,  324; 
salt,  324;  see  Fish. 

Coeflficients  of  digestibility,  75,  306. 

Coffee,  333. 

Combustion,  heat  of,  1 19 ;  of  hydrogen, 
121;  of  carbon,  121;  of  carbohy- 
drate, 122,  123;  of  proteins,  122, 
123;  of  fats,  122,  123;  and  compo- 
sition of  typical  compounds,  table, 
123. 

Comparative  economy  of  foods,  table, 
315-    _  ?i«       ^ 

Composition  and  heats  of  combustion 
of  typical  compounds,  table,  123. 

Composition  of  animal  fat,  20;  of 
edible  portion  of  food  materials, 
table,  43 ;  of  foods,  298 ;  of  human 
body,  260 ;  ultimate  of  typical  pro- 
teins, table,  35. 

Conjugated  proteins,  28. 

Consomme,  canned,  324. 

Cooking,  effect  on  digestibility,  305. 

Cook,  on  phytates  and  phosphates,  275. 

Com,  43,  128,  29s;  green,  324,  339; 
meal,  128,  251,  324,  333,  339;  sweet, 
251;  sweet,  dried,  333 ;  sweet,  fresh, 
333- 

Cowpeas,  324. 

Crackers,  Boston,  322;  butter,  324; 
cream,  324;  graham,  324;  soda, 
324,  333,  339;  water,  324. 

Cranberries,  324,  333,  339. 

Craving  for  salt,  263. 

Cream,  251,  324,  333,  339. 

Creatinin  in  protein  metabolism,  in; 
amount  in  urine,  115. 

Cremer,  on  fat  formation  from  protein, 
109. 

Cresol,  82, 

Cucumbers,  324,  333,  339. 

Currants,  43,  129 ;  dried,  324,  333,  339; 
fresh,  324,  333,  339;  juice,  333. 

Custard  pie,  328. 

Cystin,  amounts  from  proteins,  39,  301 ; 
structure,  37. 


346 


INDEX 


Dandelion  greens,  333. 

Dates,  324,  333,  339. 

Derived  proteins,  28. 

Dextrin,  14. 

Dextrose,  see  Glucx)se. 

Diabetes,  carbohydrate  from  protein  in, 
107  ;  caused  by  removal  of  pancreas, 
87  ;  effect  on  glucose,  7. 

Diabetic  sugar,  see  Glucose. 

Diamine  acids,  structure,  37. 

Diastase,  liver,  52;  malt,  14;  muscle, 
52. 

Diet,  effect  on  food  requirement,  145; 
effect  on  resistance  to  poisons,  313; 
effect  on  urine,  115;  enjoyment  of  as 
a  factor,  306 ;  in  relation  to  mineral 
metabolism,  312;  influence  on  pro- 
tein metabolism,  176,  177;  necessity 
of  calcium  in  children's,  288;  pro- 
tein, opinions  regarding  the  value 
of  liberal,  221 ;  salt-free,  264, 
292. 

Dietaries,  calcium  in,  289 ;  compiled  by 
Lang  worthy,  208;  iron  in,  252; 
phosphorus  in,  281,  282. 

Dietary  standards,  205-213;  and  food 
habits,  205  ;  references,  230. 

Dietary  studies  as  indication  of 
food  requirements,  133-135 ;  Lang- 
worthy's  table,   208. 

Digestibility,  coefficients  of,  306;  of 
beef,  effect  of  cooking,  305 ;  of  food, 
76,  307  ;  of  foods,  factors  influencing, 
77 ;  methods  of  testing,  304 ;  psychic 
influence  on,  306. 

Digestion,  artificial,  304;  behavior  of 
food  in,  303;  in  large  intestine,  72; 
in  small  intestine,  64;  in  stomach, 
56 ;  gastric,  mechanism  of,  59 ;  gas- 
tric of  proteins,  icxj ;  intestinal,  loi ; 
losses  in,  125  ;  of  carbohydrates,  84; 
of  fat,  94;  of  protein,  100;  refer- 
ences, 82 ;  salivary,  55 ;  saUvary 
in  stomach,  60 ;  work  of,  148. 

Digestive  tract,  course  of  food  through, 
55- 

Dipeptids,  24. 

Di  saccharides,  6,  9. 

Duclaux,  on  terminology,  of  enzymes, 
48. 


Economy  and  nutritive  value  of  foods,' 
298,  314,  316,  317.      ^  ' 

Edestin,  fed  with  inorganic  phosphorus, 
272  ;  ultimate  composition,  35. 

Edible  organic  nutrients  and  fuel  values 
of  foods,  table,  319;  portion  of 
foods,  42. 

Efficiency,  effect  of  fatigue,  159;  me- 
chanical, of  man,  158,  159. 

Egg  albumen,  hydrolysis,  301 ;  ulti- 
mate composition,  35. 

Eggs,  43,  128,  251,  282,  288,  295,  315, 
324,  333,  339;  iron  in,  253;  egg- 
white,  333 ;  egg-yolk,  333. 

Ehrstrom,  on  relative  value  of  casein 
and  phosphate,  272. 

Elements,  acid-  and  base-forming,  in 
foods,  29s;  inorganic,  in  body, 
261. 

Endive,  333. 

Energy  balance  in  studying  nutritive 
value  of  foods,  309. 

Energy  expended  in  digestion  and 
assimilation,  148,  149. 

Energy,  metabolism,  calculation  of, 
139;  requirement  in  metabohsm, 
132;  requirement  of  body,  118,  148; 
requirement  of  body,  references,  147, 

175- 

Enterokinase,  51,  68. 

Enzyme  action,  reversibility  of,  51. 

Enzymes,  amylolytic,  47 ;  and  their 
actions,  44 ;  as  catalyzers,  45  ;  auto- 
lytic,  53,  104 ;  classification  of,  45 ; 
coagulating,  48;  deaminizing  48; 
digestive,  48,  52;  extraceUular,  45; 
glycolytic  of  muscles,  87  ;  hydrolytic, 
47 ;  intraceUular,  45  ;  lipolytic,  47 ; 
of  nutrition,  52;  oxidizing,  48,  114; 
properties  of,  49;  proteolytic,  47; 
reducing,  48;  references,  54;  speci- 
ficity of,  46;  sugar-splitting,  47; 
terminology  of,  48. 

Equilibrium,  calcium,  288;  iron,  247; 
nitrogen,  181,  186;  phosphorus, 
279. 

Erepsin,  49,  53,  69. 

Erucic  acid,  19. 

Ethereal  sulphate,  77. 

Excelsin,  301. 


INDEX 


347 


Factor  for  proteins,  25. 

Factors  for  fuel  value,  125, 

Flack,  on  influence  of  age  on  metabo- 
lism, 169;  on  protein  metabolism  in 
fasting,  178. 

Fasting,  influence  of  previous  diet  on 
nitrogen  elimination,  177;  energy- 
metabolism  in,  150,  151,  152;  pro- 
tein metabolism  in,  179. 

Fat,  animal,  composition  of,  20 ;  body, 
formation  from  food  fat,  96;  body, 
variations  in,  21 ;  burned  as  fuel, 
95 ;  composition  of  different  mam- 
mals, 22;  digestion,  94;  emulsifica- 
tion  in  intestines,  65  ;  fate  in  metab- 
olism, 93 ;  formation  from  protein, 
108;  formation  of  carbohydrate 
from,  98;  hydrolysis  by  enzymes, 
52 ;  of  milk,  formation  from  pro- 
tein, 109;  production  from  carbo- 
hydrate, 90;  stored,  influence  on 
protein  metabolism  in  fasting,  177. 

Fats,  chemical  composition,  16;  heat 
of  combustion,  122,  123;  metabo- 
lism of,  references,  116;  phosphor- 
ized,  270;  properties  of,  16;  pro- 
tein-sparing power,  185;  references, 
40;  respiratory  quotient,  89;  sa- 
ponification of,  16. 

Fatty  acids,  17,  94. 

Fatty  oils,  properties,  16. 

Feces,  72,  74;  calcium  in,  286;  iron  in, 
232,  237,  246;  phosphorus  in,  277, 
278. 

Ferments,  action  of,  44. 

Fermentation,  excessive  in  digestive 
tract,  82. 

Ferments,  organized,  44;  references, 
54;  soluble,  see  Enzymes;  unor- 
ganized, see  Enzymes;  uricolytic, 
114. 

Figs,  324,  333,  339- 

Fischer,  hydrolysis  of  gelatin,  39;  on 
specificity  of  enzymes,  47 ;  on  poly- 
peptids,  synthesis  of,  24. 

Fish,  333,  334,  339- 

Fixed  oils,  see  Fatty  Oils. 

Flaxseed,  334. 

Flounder,  324,  325. 

Flour,  315,  334,  341 ;  barley,  251 ;  low 


grade,  288;  patent,  282;  wheat, 
29s,  251 ;  wheat,  California,  fine, 
325;  entire,  325;  graham,  325;  low 
grade,  325;  patent-roller  '  process, 
325;  straight  grade,  325;  5ce  Buck- 
wheat, etc. 

Folin,  on  nitrogen  in  urine,  115;  on 
protein  metabolism,  223 ;  on  sulphur 
metabolism,  269. 

Food,  behavior  in  digestion,  55,  303 ; 
calcium  in,  286  ;  consumption,  influ- 
ence on  metabolism,  150;  course  of 
through  digestive  tract,  55  ;  digesti- 
bility of,  76;  methods  of  testing, 
304;  digestibility  of,  psychic  influ- 
ence, 306;  fuel  value  of,  118,  125, 
126 ;  loo-calorie  portions,  table,  128 ; 

.  fuel  value  of,  references,  147  ;  habits 
and  dietary  standards,  205 ;  habits 
and  dietary  standards,  references, 
230;  iron  in,  231;  food  materials, 
acid-  and  base-forming  elements, 
29s;  materials,  calcium  in,  table, 
290;  materials,  composition  of 
edible  portion,  table,  43 ;  material, 
loo-calorie  portions,  128 ;  phosphorus 
in,  281,  282;  nutritive  ratio  of, 
130;  passage  into  the  intestines,  62  ; 
passage  through  stomach,  61 ;  re- 
quirement, as  indicated  by  balance 
or  metabolism  experiments,  138,  141 ; 
requirements  as  indicated  by  calo- 
rimeter experiments,  142,  145 ;  re- 
quirements as  indicated  by  dietary 
studies,  133,  134,  13s ;  requirements 
as  indicated  by  respiration  experi- 
ments, 135 ;  requirements  as  influ- 
enced by  temperature,  164;  re- 
quirements, average,  146;  require- 
ments, conditions  affecting,  148; 
requirements,  conditions  affecting, 
references,  175;  requirements  for 
different  ages,  174;  requirements 
for  children,  172;  requirements  for 
men  and  women,  172  ;  requirements, 
individual  differences,  146;  re- 
quirement, influence  of  age  and  sex, 
168,  172;  of  muscular  work,  154, 
15s  ;  of  size  and  shape  of  body,  165 ; 
requirement,  references,  147. 


348 


INDEX 


Foods,  ash  constituents  of,  260,  267, 
282,  290,  295,  332,  338;  ash  con- 
stituents of,  in  percentage  of  edible 
portion,  332  ;  in  loo-calorie  portion, 
338;  comparative  economy  of, 
table,  315;  composition,  41,  298, 
319;  digestibility,  76,  303;  fuel 
values  of,  table,  319;  general  com- 
position, 41,  54;  iron  in,  referen  es, 
259;  iron  in,  table,  251;  market 
cost  vs.  nutritive  value,  316;  nu- 
tritive value  and  economy,  298; 
nutritive  value  and  economy,  refer- 
ences, 316-317;  partial  analyses, 
misleading  results  of,  299;  rate  of 
passage  through  digestive  tract,  71 ; 
relation  of  sulphur  to  protein  in,  267. 

Foodstuffs,  fate  of  in  metabolism,  84, 
116;  inorganic  in  metabolism,  260; 
inorganic,  references,  296;  non- 
nitrogenous,  nutritive  value  of,  309 ; 
organic,  4;  specific  dynamic  action, 
152. 

Forbes,  on  effects  of  different  rations, 
313.  317;  on  phosphorus  in  diet, 
269;  on  phytates  and  phosphates, 
27s  ;  on  value  of  phosphates,  273. 

Formaldehyde  formation  in  plants,  5 

Fructose,  7. 

Fniits,  acidity  and  ash  constituents, 
296 ;  as  source  of  iron,  256 ;  digesti- 
bility, 76. 

Fruit  sugar,  7. 

Fuel  requirements,  see  Food  Require- 
ments, Dietary  Standards. 

Fuel  value  of  food,  118,  125,  127,  129, 
147,  319- 

Fuel  value,  standards  for  dietaries,  213. 

Galactans,  8,  310. 

Galactose,  8, 

Gastric  digestion,  59,  100. 

Gastric  juice,  59,  62,  63. 

Gaule,  on  absorption  of  inorganic  iron, 

238. 
Gautier,  on  dietary  standard,  206;   on 

calcium  requirement,  289. 
Gelatin,  39,  302,  316,  325. 
GUadin,  30;  hydrolysis,  301 ;  ultimate 

composition,  35. 


Globin,  33,  39, 

Globulins,  26,  30. 

Glucose,  7  ;  metabolism  of,  86,  108. 

Glutamic  acid,  amounts  from  proteins, 

39,  301 ;  structure,  37. 
Glutelins,  27,  30. 
Gluten,  30. 
Glutenin,  30,  301. 
Glycerides,  17. 
Glycin,  amounts  from  proteins,  39,  301 ; 

formation     in     metaboUsm,      302 ; 

structure,  23,  36. 
Glycocoll,  see  Glycin. 
Glycogen,  j[4j_86,  90,  106. 
Glycolytic  enzymes,  52,  87. 
Glycoproteins,  28. 
Glycosuria,  7. 
Glycyl-glycin,  23. 
Goodall  and  Joslin,  on  ash-free  diet, 

293. 
Gottlieb,   on   metaboUsm  of  injected 

iron,  235. 
Grain  products  as  source  of  iron,  255. 
Grapes,  325,  334,  339- 
Grapefruit,  334. 
Grape  sugar,  see  Glucose. 
Grindley,  on  artificial  digestion  of  beef, 

305. 
Griitzner,  on  digestion  in  stomach,  58. 
Guanase,  53,  114. 
Gumpert,  on  phosphorus  metabolism, 

272. 

Haddock,  325,  334,  339. 

Hagler,  on  relation  of  weight  to  height, 
214. 

Hahbut,  301,  325,  334,  339. 

Hahburton  and  Hopkins,  on  terminol- 
ogy of  proteins,  25. 

Haliburton,  on  protein  in  diet,  225. 

Ham,  43,  128,  32s,  335.  340. 

Hammarsten,  on  foodstuffs,  40;  on 
protein  metaboUsm,  204 ;  on  rennin, 

45- 

Hart,  on  phosphorus  metaboUsm,  269, 
273,  275,  280,  297. 

Hartley,  on  fatty  acids,  23. 

Hausermann,  on  utilization  on  inor- 
ganic iron,  240. 

Heat  of  combustion,  see  Combustion. 


INDEX 


349 


Heat  production,  see  Metabolism. 
Hematin,  33. 
Hemoglobin,  28,  33,  253. 
Henriques,  on  nitrogen  equilibrium  with 

amino  acids,  103. 
Henriques  and  Hansen,  on  variation  in 

body  fat,  21. 
Herring,  325,  334,  339- 
Herter,   on   bacteria  of  the  digestive 

tract,  80;    on  calcium  metabolism, 

287. 
Heterocyclic  amino  acids,  38. 
Hill,    C,   on   reversibility   of  enzyme 

action,  51. 
Hill,  L.,  on  carbohydrate  from  fat,  98; 

on  relation  of  weight  to  height  and 

age,  174,  215. 
Hippuric  acid  in  protein  metabolism, 

III. 
Histidin,  amoimts  from  proteins,  39, 

301 ;  structure,  38. 
Histones,  27. 
Hoffmann,  on  body  fat  from  food  fat, 

97- 

Honey,  7,  326,  334,  339. 

Hordein,  39. 

Hormone,  64,  67. 

Hosslin,  on  body  surface  and  heat 
production,  166. 

Howell,  on  amino  acids  in  blood,  103 ; 
on  enzymes,  47,  52 ;  on  intestinal 
absorption,  70 ;  on  salts  in  the  body, 
285  ;  on  secretion  of  gastric  juice,  58. 

Huckleberries,  326,  334,  339. 

Human  body,  elementary  composition, 
260. 

Human  fat,  22. 

Hunt,  on  diet  and  resistance  to  poisons, 
313. 

Hutchison,  on  comp)osition  of  food,  54 ; 
on  food  requirements,  175;  on  pro- 
tein in  diet,  222,  223. 

Indican,  82. 

Individual  differences  in  food  require- 
ment, 146. 

Indol,  82. 

Infants,  see  Children. 

Inorganic  elements,  231,  234,  260,  296, 
see  also  Ash  Constituents. 


Intestinal  digestion,  64-73,  85,  94,  loi. 

Intestinal  juice,  52,  53,  64. 

Intestinal  movements  in  digestion,  65, 
72. 

Inulin,  310. 

Inversion  of  sucrose,  10. 

Invertase,  10,  52,  69. 

Invert  sugar,  10. 

Iodine  of  diet  in  relation  to  resistance, 
314. 

Iron,  action  of  medicinal  and  food  iron 
compared,  237-246;  balance  in  study 
of  food  values,  312;  in  body,  249; 
in  dietaries,  252;  in  foods,  231,  250- 
259,  332-341;  in  hemoglobin,  35, 
253 ;  in  milk  and  young,  249 ;  me- 
tabolism, 232-250;  necessity  for,  231, 
245  ;  requirement  of  body,  245-250 ; 
utilization  of  different  forms,  234- 
245,  252-259. 

Jordan  and  Jenter,  on  milk  fat   from 

carbohydrate  food,  92. 
Jordan,  Hart,  and  Patten,  on  phytates 

and  phosphates,  275,  297. 

Kauffmann,  on  food  value  of  gelatin, 

302. 
Kayser,  on  protein-sparing    action  of 

fat  and  carbohydrates,  186. 
Keller,  on  food  value  of  phosphates,  272. 
Klemperer,  on  protein  requirement,  192. 
Kulz,  on  glycogen  from  protein,  106. 
Kunkel  and  Egers,   on  formation  of 

hemoglobin,  239. 

Lact-albumin,  35. 

Lactase,  11,  49,  52,  69. 

Lactic  acid,  86. 

Lactose,  11. 

Lamb,  composition  of  different  cuts, 
326. 

Landergren,  on  protein-sparing  action 
of  fat  and  carbohydrate,  189. 

Langworthy,  on  dietary  studies,  208; 
on  dietary  standard,  210. 

Laurie  acid,  18. 

Lawes  and  Gilbert,  on  fat  from  carbo- 
hydrate, 91. 

Lecithans,  270. 


350 


INDEX 


Lecithins,  270, 

Lecithoproteins,  28,  270. 

Legumes,  digestibility,  76. 

Legumin,  35.  30i. 

Leipziger,  on  phosphorus  metabolism, 
271. 

Lemons,  326,  334,  339. 

Lentils,  334,  340. 

Lettuce,  43,  128,  326,  334,  340. 

Leucin,  amounts  from  proteins,  39, 
301 ;  structure,  37. 

Leucosin,  35,  301. 

Levin,  on  bacteria  in  the  digestive 
tract,  79. 

Levulose,  see  Fructose. 

Linoleic  acid,  20. 

Linolenic  acid,  20. 

Lipases,  47,  49,  52,  94. 

Lipolytic  enzymes,  see  Lipases. 

Lippmann,  on  terminology  of  enzymes, 
48. 

Liver,  52,  85,  326. 

Lorisch,  on  absorption  of  galactan,  311 ; 
on  utilization  of  cellulose,  311. 

Lunin,  on  acid-forming  diet,  292. 

Lusk,  on  carbohydrate  from  alanin, 
108 ;  from  protein,  104 ;  on  protein- 
sparing  action  of  carbohydrate,  185; 
relation  of  temperature  to  metabo- 
lism, 164. 

Lysin,  amounts  from  proteins,  39,  301 ; 
structure,  37. 

Macallum,  on  iron  metabolism,  238. 
McCollum,  on  phosphorus  metabolism, 

273. 
Magnesium,  261,  283. 
Magnus-Levy,    on    food    requirement, 

137 ;   on  influence  of  age  and  sex  on 

metaboHsm,  169,  171;  on  respiratory 

quotient,  90. 
Maltase,  49,  52,  69. 
Maltose,  11. 

Malt  sugar,  see  Maltose. 
Mannans,  digestibility,  310. 
Marcuse,  on  utilization  of  phosphorus 

of  casein,  271. 
Maxwell,  on  phosphorized  fat,  271. 
Meat,  335,  340 ;  extracts,  335  ;  sauces, 

335  ;  iron  in,  252. 


Mechanical  eflBciency  of  man,  158,  159. 

Meischer,  on  phosphorized  proteins, 
271. 

Meltzer,  on  functions  of  calcium,  285 ; 
on  protein  in  diet,  226. 

Mendel  and  Nakaseko,  on  digestibility 
of  inulin,  310. 

Mendel  and  Swartz,  on  digestibility  of 
galactans,  310. 

Mendel,  on  uric  acid  formation  in  body, 
114. 

Metabolism,  behavior  of  foods  in,  308 ; 
conditions  affecting,  references,  175; 
energy  requirement  in,  132;  fate  of 
carbohydrates  in,  84 ;  fate  of  fat  in, 
93 ;  fate  of  foodstuffs  in,  references, 
116;  fate  of  proteins  in,  100;  influ- 
ence of  age  and  sex  on,  168;  influ- 
ence of  food  consumption,  150;  in- 
fluence of  muscular  work,  154,  155; 
influence  of  size  and  shape  of  body, 
165;  influence  of  temperature,  163; 
in  relation  to  body  surface,  167; 
mineral,  260;  mineral,  references, 
296 ;  of  ammonium  salts,  1 1 1 ;  of 
chlorides,  262;  of  creatinin,  11 1; 
of  energy,  calculation  of,  139;  of 
iron,  235 ;  of  nitrogen,  1 10 ;  of 
phosphorus,  269,  275 ;  of  purin  bod- 
ies, III ;  of  sulphur  compounds,  265, 
266,  268;  of  urea,  iii ;  protein,  138, 
176;  influence  of  muscular  exercise, 
197;  protein,  references,  203;  purin, 
114. 

Metaproteins,  28. 

Milk,  condensed,  327;  skimmed,  327; 
whole,  43,  128,  251,  -282,  288,  295, 
315,  327,  335,  340;  as  source  of 
protein  for  children,  202 ;  iron  in, 
249,  253,  254;  of  different  species, 
274;  sugar,  see  Lactose. 

Mineral  metabolism,  260;  mineral 
metabohsm,  references,  296. 

Molecular  weights  of  proteins,  35. 

Monoamino  acids,  dibasic,  37 ;  mono- 
basic, 36. 

Monosaccharides,  5,  6. 

Moore  and  Bergin,  on  reaction  of 
intestinal  contents,  69. 

MortaUty,  relation  to  body  weight,  217. 


INDEX 


351 


Moulton  and  Trowbridge,  on  variation 
in  body  fat,  2 1 . 

Munk,  on  body  fat  from  food  fat,  g6. 

Murlin,  on  food  value  of  gelatin,  316. 

Muscle  diastase,  52;  glycolytic  en- 
zyme of,  87. 

Muscular,  tension  (tone),  work  of,  149 ; 
work  and  metabolism,  154,  155,  156, 
197- 

Mutton,  composition  of  different  cuts, 

327,  335- 
Myosin,  fed  with  inorganic  phosphorus, 

272  ;  ultimate  composition,  35. 
Myristic  acid,  18. 

Nectarines,  327. 

Neumann,  on  food  requirement  as  indi- 
cated by  dietary  studies,  134 ;  on  pro- 
tein requirement,  192. 

Nitrogen  balance,  139,  140;  equilib- 
rium as  indication  of  protein  require- 
ment, 181 ;  excreted  by  kindneys, 
112;  factor  for  proteins,  25;  in 
metabolism,  no. 

Nitrogenous  fats,  24. 

Nuclease,  114. 

Nucleic  acid  from  nucleoproteins,  32. 

Nucleoalbumins,  see  Phosphoproteins. 

Nucleoproteins,  28,  31;  occurrence  in 
body,  276. 

Nutrients,  edible  organic,  and  fuel 
values  of  foods,  table,  319. 

Nutritive  ratio,  130. 

Nutritive  value  and  economy  of  foods, 
298;  references,  316,  317;  of  non- 
nitrogenous  foodstuffs,  309;  of 
organic  and  inorganic  phosphorus, 
272  ;  and  market  cost  of  food,  316. 

Nuttall  and  Thierfelder,  on  bacteria  of 
digestive  tract,  79. 

Oatmeal,  43,  128,  251,  282,  288,  295, 

315,  327,  335,  340. 
ObendoerfFer,  on  calcium  requirement, 

289. 
Oleic  acid,  19. 
Olive  oil,  43,  129,  315. 
Olives,  327,  328,  335,  340. 
Onions,  328,  335,  340. 
Oppenheimer,  on  enzymes,  47. 


Oranges,  43,  129,  282,  288,  328,  335, 

340. 
Organic  foodstuffs,  4. 
Ornithin,  in  protein  metabolism,  11 1; 

structure,  37. 
Osborne,  on  hydrolysis  of  proteins,  39, 

301 ;    on  sulphur  in    proteins,   266 ; 

on  ultimate  composition  of  proteins, 

35- 
Oshima,   on  digestibility  of    mannan, 

310. 
Ovalbumin,  301. 

Ovovitellin,  301 ;  as  source  of  phos- 
phorus, 272;    ultimate  composition, 

35. 
Oxidases,  48,  53 ;  in  tissues,  87. 
Oxygen,  consumed  by  body,  88. 
Oxyhemoglobin,  ultimate  composition, 

35- 
Oxyprolin,  amounts  from  proteins,  39, 

301. 

Palmitic  acid,  18. 

Pancreas,  internal  secretion,  87. 

Pancreatic  amylase,  52;  duct,  66; 
juice,  66. 

Parsnips,  282,  288,  328,  335,  340. 

Paton,  on  formation  of  phosphorized 
proteins,  271. 

Pawlow,  on  psychic  secretion,  63,  306. 

Peaches,  43,  129,  328,  335,  340. 

Peanuts,  43,  129,  282,  288, 328,336,  340. 

Peas,  canned,  328;  cowpeas,  336,  340; 
dried,  251,  282,  288,  328,  335,  340; 
green,  295,  328,  335,  340;  soup, 
canned,  328. 

Pepsin,  49,  53  ;  action  on  proteins,  loi. 

Peptids,  29 ;  composition  of,  24 ;  rela- 
tion to  peptones,  34. 

Peptones,  properties,  29;  commercial, 
2,2,;  composition,  2,2>- 

Peristalsis,  stomach,  55,  60;  intestinal, 
65. 

Petit,  on  pepsin,  45. 

Pettenkofer  and  Voit,  on  method  for 
carbon  balance,  137. 

Pfliiger,  on  fat  formation  from  protein, 
109 ;  on  protein  as  source  of  muscu- 
lar energy,  105. 

Phaseolin,  301. 


352 


INDEX 


Phenol,  82. 

Phenylalanin,  amoxints  from  proteins, 
39,  301 ;  structure,  37. 

Phloridzin  diabetes,  carbohydrate  from 
protein,  107. 

Phosphates,  270;  see  also  Phosphorus. 

Phosphoproteins,  28,  32;  digestion 
and  absorption,  272. 

Phosphoric  acid  derivatives,  270. 

Phosphorized  fats,  270,  271 ;  proteins, 
270,  271 ;  see  also  Phosphorus. 

Phosphorus,  balance  in  study  of  food 
values,  312;  with  diflferent  amounts 
in  food,  278 ;  compounds,  occurrence 
and  metabolism,  269,  270;  ehmina- 
tion,  277;  equilibrium,  279;  func- 
tions in  body,  277;  in  diet,  269; 
in  food  materials  and  typical  die- 
taries, 281,  282  ;  in  milk  of  different 
species,  274;  organic  and  inorganic, 
value  of,  272,  273 ;  metaboUsm  in 
man,  275 ;  of  phosphoproteins,  32 ; 
requirement,  278;  significance  in 
growth,  269. 

Phycetoleic  acid,  19. 

Physiological  fuel  value  of  food  con- 
stituents, 125. 

Phytates,  270;  nutritive  value  of,  274. 

Phytic  acid,  270. 

Pineapples,  canned,  329 ;  fresh,  43, 129, 
288,  329,  336,  340;  juice,  336. 

Playfair's  dietary  standard,  206. 

Plums,  43,  129,  329,  336,  340. 

Poisons,  effect  of  diet  on  resistance  to, 
313- 

Polypeptids,  synthesis  of,  24.  . 

Polysaccharides,  6,  12. 

Pork,  composition  of  different  cuts,  315, 
329.  335,  336. 

Portal  vein,  85. 

Portions,  loo-calorie  of  food  materials, 
126,  128. 

Potassium,  amount  in  body,  261 ;  dis- 
tribution in  body,  283;  function  in 
body,  262. 

Potatoes,  43,  128,  251,  282,  288,  295, 
315,  329,  336,  340;  sweet,  329,  336, 
340. 

Pottevin,  on  reversibility  of  pancreatic 
lipase,  52, 


Prausnitz,  on  feces  from  different  diets, 
74. 

Primary  protein  derivatives,  28. 

Prolin,  amounts  from  proteins,  39,  301 ; 
structure,  38. 

Protamins,  27. 

Proteans,  28. 

Protein,  dietary  standards,  219;  diet, 
effect  on  urine,  115;  diet,  opinions 
regarding,  221  ;  kataboUsm,  adjust- 
ment to  protein  supply,  183 ;  me- 
tabolism, amino  acids  in,  in;  me- 
tabolism and  requirement,  176;  refer- 
ences, 203;  metabolism,  "factor  of 
safety"  in,  227;  metabolism  in 
fasting,  177;  influence  of  glycogen 
and  body  fat,  178 ;  metabolism,  influ- 
ence of  muscular  exercise,  197 ;  me- 
tabolism, sulphur  in,  266 ;  nomencla- 
ture, 26;  relation  to  fuel  value,  220; 
requirement,  181,  197;  requirement 
as  affected  by  diet,  192-197;  re- 
quirement, influence  of  growth,  202 ; 
requirement,  references,  230;  "pro- 
tein-sparing" power  of  fats  and  car- 
bohydrates, 185-191 ;  synthesis  by 
autolytic  enzymes,  104 ;  see  also  Pro- 
teins. 

Proteins,  23,  24,  26,  35,  39,  301 ;  a'co- 
hol-soluble,  26, 30 ;  amino  acids  in,  39, 
301 ;  amount  and  functions  in  ordi- 
nary diet,  228,  229;  as  body  fuel 
IDS ;  chemical  analysis  of,  300 ; 
coagulated,  28;  conjugated,  28; 
digestion  products,  loi ;  factor  for, 
25  ;  fate  in  metabohsm,  100;  forma- 
tion of  carbohydrate  from,  106; 
formation  of  fat  from,  108;  forma- 
tion of  urea  from,  in;  gastric  di- 
gestion of,  100 ;  heat  of  combustion, 
122,  123;  hydrolysis  by  enzymes, 
33 ;  intestinal  digestion,  loi ;  me- 
tabolism references,  116;  molecular 
weights,  35 ;  percentages  of  amino 
acids  from,  39,  301 ;  phosphorized, 
270,  271;  primary  derivatives,  28; 
ratio  of  nitrogen  to  sulphur  in,  266 ; 
references,  40;  relation  to  sulphur, 
267 ;  respiratory  quotient,  89 ;  sec- 
ondary derivatives,  28;   simple,  26; 


INDEX 


353 


specific  dynamic  action,  153;  struc- 
ture, 36,  39,  301 ;  structure  in  rela- 
tion to  food  value,  302 ;  ultimate 
composition  of,  table,  35;  see  also 
Protein. 

Proteolytic  enzymes,  47. 

Proteoses,  29,  33. 

Prunes,  43,  129,  251,  282,  288,  295,  315, 
329,  336,  340. 

Psychic  influences  on  digestion,  306; 
secretion  of  gastric  juice,  63. 

Ptyalin,  13,  49,  52,  84. 

Purins,  32;  formation  in  metabolism, 
111,113;  hydrolysis  by  enzymes,  S3, 
114. 

Putrefaction  in  digestive  tract,  82. 

Pyrimidin  derivatives  from  nucleo- 
proteins,  32. 

Raisins,  43,   129,   251,  315,  329,  336, 

341. 

Rate  of  passage  of  diflferent  foods 
through  digestive  tract,  71. 

Reductases,  45. 

Regulation  of  temperature,  163. 

Relation  of  weight  to  height,  214,  215, 
216,  217. 

Requirement,  calcium,  287  ;  iron,  245 ; 
phosphorus,  278;  protein,  176,  181; 
protein,  references,  203 ;  sulphur, 
268 ;  see  also  Food  Requirement. 

Resorption  from  intestines,  70. 

Respiration,  experiments,  135 ;  work 
of,  149. 

Respiratory  quotient,  136;  as  evidence 
of  conversion  of  carbohydrate  to 
fat,  92  ;  as  evidence  of  conversion  of 
fat  to  carbohydrate,  98;  for  carbo- 
hydrates, 88;  for  fats,  88;  for  pro- 
teins, 89. 

Rice,  43,  128,  251,  282,  288,  29s,  330, 
336,  341- 

Rohmann,  on  organic  and  inorganic 
phosphorus,  272. 

Rubner,  on  factors  for  fuel  value,  127; 
on  fuel  values  of  food  constituents, 
125;  on  influence  of  body  surface 
on  metaboHsm,  166;  on  metabolism 
in  fasting,  152;  on  specific  dynamic 
action. 


Rutgers,  on  comparison  of  animal  and 
vegetable  proteins,  308, 

Saccharose,  see  Sucrose. 

Saliva,  55. 

Salivary  amylase,  52;    digestion,  55; 

digestion  in  stomach,  60;  glands,  55. 
Salmon,  43,  128,  330,  334,  339. 
Salt,   craving  for,   263 ;    use  of,   262 ; 

salt-free  diet,  excretion  of  chlorine 

on,  264. 
Sandmeyer,  on  digestibility  of  inulin, 

310. 
Saponification  of  fats,  16. 
Sawamura,   on   mannase   in   digestive 

tract,  310. 
Schondorff,  on  distribution   of   glyco- 
gen in  body,  15. 
Schulze  and  Castro,  on  galactans,  8. 
Schulze  and  Reineke,  on  composition 

of  fat  of  different  mammals,  28. 
Secondary  protein  derivatives,  29, 
Secretin,  67. 
Seegen,    on    carbohydrate    formation 

from  liver  protein,  107. 
Selensky,  on  iron-free  diet,  236. 
Serin,  amounts  in   proteins,  39,  301 ; 

structure,  37. 
Serum-globulin,  ultimate  composition, 

35- 
Sex,  influence  on  food  requirement,  168. 
Sherman,  on  iron  requirement,  247. 
Siven,  on  protein  requirement,  193. 
Size  and  shape  of  body,  influence  on 

metabolism,  165. 
Skatol,  82. 
Snell,  on  Atwater  bomb    calorimeter, 

119. 
Socin,  on  metabolism  of  iron,  235. 
Sodium,   amount  in  body,    261 ;    dis- 
tribution in  body,  283 ;   function  in 

body,  262. 
Soldner,  on  phosphorus  in  human  milk, 

273. 
Sonden    and    Tigerstedt,     metabolism 

experiments,    141 ;     on  influence   of 

age  on  metabolism,  170. 
Specific  dynamic  action  of  foodstuffs, 

149,  152,  153. 
Spinach,  43,  128,  251,  330,  336,  341. 


2A 


354 


INDEX 


Standards,  dietary,  205 ;  dietary,  refer- 
ences, 230;  for  fuel  value,  213;  for 
protein  in  dietary,  2iq;  lOO-calorie 
portions  of  food  materials,  table,  128. 

Stirch,  12;  soluble,  13;  sugar,  see 
Glucose. 

Starling,  on  formation  of  carbohydrate 
from  fat,  99;  on  hormone  causing 
gastric  secretion,  64. 

Stearic  acid,  18. 

Steinitz,  on  organic  and  inorganic 
phosphorus,  271. 

Stockman,  on  absorption  of  inorganic 
iron,  237. 

Stoklasa,  on  lecithin  in  human  milk. 
274. 

Stomach,  digestion  of  fat,  94;  move- 
ments in  digestion,  56,  59;  passage 
of  food  through,  61. 

Strawberries,  43,  330,  336,  341. 

Succus  entericus,  64. 

Sucrase,  10,  49. 

Sucrose,  fate  in  body,  10;  hydrolysis, 
10 ;  occurrence  and  properties,  9. 

Sugar,  128,  315,  330 ;  cane,  see  Sucrose ; 
invert,  10;  milk,  see  Lactose. 

Sulphate,  conjugated,  77 ;  ethereal,  77  ; 
ethereal  in  urine,  268. 

Sulphur,  excretion  of,  269 ;  in  different 
proteins,  266 ;  in  foods,  267,  332, 
338;  occurrence  and  metabolism, 
268;  in  body,  261,  268;  require- 
ment, 268. 

Symonds,  on  relation  of  weight  to 
height,  217 ;  on  relation  of  weight  to 
mortality,  217. 

Synthesis,  of  carbohydrates  in  plants, 
4 ;  of  polypeptids,  24 ;  of  protein  by 
autolytic  enzymes,  104. 

Tallquist,  on  protein-sparing  p)ower  of 
fats  and  carbohydrates,  188. 

Tartakowsky,  on  utilization  of  inor- 
ganic iron,  244. 

Taylor,  on  ash-free  diet,  293. 

Temperature,  influence  on  metabolism 
163  ;  regulation  of,  163. 

Terminology  of  proteins,  25. 

Test  meals  in  determining  digestibility, 
305. 


Thio-amino  acids,  structure,  38, 

Thrombase,  47. 

Thrombin,  47. 

Tigerstedt,  on  food  requirements    for 

different   kinds  of   work,    162 ;     on 

influence  of  age  on  metabolism,  168; 

on  metabolism  in  fasting,  151. 
Tomatoes,  canned,  330 ;  fresh,  43,  129, 

330,337;  juice,  337. 
Tripeptids,  24. 
Trypsin,  49,  53,  69 ;  action  on  proteins, 

lOI. 

Trypsinogen,  50,  68. 

Tryptophan,   amounts  from  proteins, 

39,  301 ;  structure,  38. 
Turnips,  43,  129,  251,  282,  288,  295, 

330,  331,  337,  341- 
Tyrosin,   amounts  from   proteins,   39, 

301 ;  structure,  37. 

Urea,   formation   from  proteins,    in; 

in  protein  metabolism,  no,  in. 
Uric  acid,  formation  in  metaboHsm,  113. 
Uricolytic  ferment,  114. 
Usher  and  Priestley,  on  carbohydrate 

synthesis  in  plants,  5. 

Valin,  amounts  from  proteins,  39,  301 ; 
structure,  37. 

Value,  nutritive,  and  economy  of  foods, 
references,  316,  317;  of  liberal  pro- 
tein diet,  opinions  regarding,  221. 

Veal,  composition  of  different  cuts,  331, 
335,  337,  340. 

Vegetables  as  source  of  iron,  256;  co- 
efficients of  digestibility,  76. 

Vein  portal,  85. 

Voit,  on  distribution  of  phosphorus  in 
body,  276 ;  on  fat  formation  from 
protein,  109;  on  food  requirement 
with  moderate  work,  155;  on  influ- 
ence of  previous  diet  on  protein 
metabolism,  177;  on  iron  metabo- 
lism, 236;  dietary  standard,  205. 

Volhard,  fat  digestion  in  stomach,  94. 

Von  Noorden,  on  establishment  of 
protein  equilibrium  after  change  of 
diet,  182,  183;  on  fat  and  carbo- 
hydrate as  "protein  sparers,"  186; 
on  food  requirements  per  kilogram. 


INDEX 


355 


173;    on  protein  in  diet,   221;    on 

relation  of  fatness  to  metabolism,  168. 

Von  Wendt,  on  iron  requirement,  247 ; 

on  value  of  inorganic  phosphate,  273. 

Wallace    and    Gushing,    on    intestinal 

absorption,  70. 
Walnuts,  282,  288,  331,  337,  341. 
Water  content  of  foods,  effect  on  fuel 

value,  129. 
Watson  and  Hunter,  on  nutritive  values 

of  different  rations,  313. 
Weight,  relation  to  height,   214,   215, 

216,  217;  relation  to  mortahty,  217. 
Weiske,  on  digestibility  of  mannan,  309. 
Wheat,    128,    282,    288;     bran,    337; 


cracked,  331 ;  entire  grain,  251,  295, 
337  ;  flour,  43,  251,  337,  341 ;  gluten 
of,  30 ;  gliadin  in,  30 ;  glutenin  in,  30. 

Wolffberg,  on  carbohydrate  from  pro- 
tein, 106. 

Woltering,  on  feeding  inorganic  iron, 
238. 

Wright,  on  diet  as  cause  of  scurvy,  293. 

Zadik,  on  organic  and  inorganic  phos- 
phorus, 271. 

Zein,  35,  301. 

Zuntz,  on  effect  of  fatigue  on  efficiency, 
159;  respiration  apparatus,  136. 

Zymase,  45. 

Zymogens,  50. 


T 


HE  following  pages  contain  a  list 
of  Macmillan  books  on  Chemistry 


A  LIST  OF  WORKS  ON  CHEMISTRY 

Published  by  The  Macmillan  Company 


KAHLENBERG.  Outlines  of  Chemistry.  A  textbook  for  college  stu- 
dents. By  Louis  Kahlenberg,  Ph.D.,  Professor  of  Chemistry  and 
Director  of  the  Course  in  Chemistry  in  the  University  of  Wisconsin.  Pub- 
lished in  New  York,  1909.  Cloth,  8vo,  548  pages,  $2.60  net 

STODDARD.  Introduction  to  General  Chemistry.  By  John  T.  Stod- 
dard, Professor  of  Chemistry  at  Smith  College,  Northampton,  Mass. 
New  York,  1910.  C7oi/i,  121110,  4j2  pages,  $1.60  net 

GOOCH  &  WALKER.  Outlines  of  Inorganic  Chemistry.  By  Frank 
Austin  Gooch,  Professor  of  Cliemistry  in  Yale  University,  and  CLAUDE 
Frederic  Walker,  teacher  of  Chemistry  in  the  High  School  of  Com- 
merce of  New  York  City.  Cloth,  514  pages,  $1.75  net 

JONES.  Principles  of  Inorganic  Chemistry.  By  Harry  C.  Jones,  Pro- 
fessor of  Physical  Chemistry  in  the  Johns  Hopkins  University.  New  York. 
Third  Edition,  1906.  Cloth,  521  pages,  $3.00  net 

JONES.  Elements  of  Inorganic  Chemistry.  By  Harry  C.  Jones,  Pro- 
fessor of  Physical  Chemistry  in  the  Johns  Hopkins  University.  New  York, 
1903.    Second  Edition,  1904.    Reprinted,  1908. 

Cloth,  i2mo,  343  pages,  $1.25  net 

OSTWALD.  The  Principles  of  Inorganic  Chemistry.  By  Wilhelm 
OsTWALD.  Translated  with  the  author's  sanction  by  Alexander  Findlay, 
M.A.,  Ph.D..  D.Sc.     London,  1902,     Third  Edition,  1908. 

Cloth,  Svo,  801  pages,  $6.00  net 

ROSCOE  &  HARDEN.    An  Inorganic  Chemistry  for  Advanced  Students. 

By  Sir  HENRY  E.  RoscoE,  F.R.S.,  and  Arthur  Harden,     London. 

Cloth,  8vo,  $1.00  net 

ROSCOE  &  SCHORLEMMER.  A  Treatise  on  Chemistry.  By  Sir  H.  E. 
RoscoE,  F.R.S.,  and  C.  Schorlemmer,  F.R.S.  Vol.  I  — The  Non- 
Metallic  Elements.    London,  1877.    Third  Edition,  1905. 

Cloth,  8vo,  Q3I  pages,  $5.00  net 
Vol.  II  — The  Metals.    London,  1878,    Third  Edition,  1897.    Fourth 
Edition,  1907.  Cloth,  8vo,  1436  pages,  $7.50  net 

Vol.  III.     Preparing. 

ROSCOE.  Lessons  in  Elementary  Chemistry,  Inorganic  and  Organic. 
By  Sir  Henry  E.  Roscoe,  D.C.L.,  L.L.D.,  F.R.S.  London,  1902.  Latest 
reprint,  1907.  Cloth,  i2mo,  523  pages,  $1.25  net 

DOBBIN  &  WALKER.  Chemical  Theory  for  Beginners.  By  Leonard 
Dobbin,  Ph.D.,  and  James  Walker,  Ph.D.,  D.Sc.  London,  1892.  Fifth 
Edition,  1906.  Cloth,  i6mo,  240  pages,  $  .70  net 


A  List  of  Works  on  Chemistry — Continued 


RAMSAY.    Experimental  Proofs  of  Chemical  Theory  for  Beginners.    By 

William  Ramsay,  Ph.D.,  LL.D.,  Sc.D.,  F.R.S.  London,  1884.  Second 
Edition,  1893.    Reprinted,  1900,  1908.         Cloth,  i8mo,  143  pages,  $  .60  net 

LENGFELD.  Inorganic  Chemical  Preparations.  By  Felix  Lengfeld, 
Assistant  Professor  of  Inorganic  Chemistry  in  the  University  of  Chicago. 
New  York,  1899.     Reprinted,  1905.  Cloth,  i2mo,  57  pages,  $  .60  net 

BENEDICT.  Chemical  Lecture  Experiments.  By  Francis  Gano  Bene- 
dict, Ph.D.    New  York,  1901.  Cloth,  izmo,  436  pages,  $2.00  net 

PERKIN  &  LEAN.  Introduction  to  the  Study  of  Chemistry.  By  W.  H. 
Perkin,  Lr.,  Ph.D.,  F.R.S.,  and  Bevan  Lean,  D.Sc,  B.A.  London, 
1896.     Seventh  reprint,  1906.  Cloth,  i2mo,  334  pages,  $  .75  net 

NERNST.  Theoretical  Chemistry  from  the  Standpoint  of  Avogadro's 
Kule  and  Thermodynamics.  By  Prof.  Walter  Nernst,  Ph.D.,  of  the 
University  of  Gottingen.  Revised  in  accordance  with  the  fourth  German 
edition.     London,  1895.     Second  EngHsh  edition,  1904. 

Cloth,  8vo,  771  pages,  $4.50  net 

OSTWALD.    The   Scientific    Foundations    of    Analytical    Chemistry. 

Treated  in  an  elementary  manner.  By  WiLHELM  Ostvvald.  Trans- 
lated with  the  author's  sanction  by  George  M.  Gowan.  London,  1895. 
Third  Edition,  1908.  Cloth,  J2mo,  247  pages,  $2.00  net 

CHESNEAU.  Theoretical  Principles  of  the  Methods  of  Analytical 
Chemistry,  based  upon  Chemical  Reactions.  By  M.  G.  Chesneau, 
Ingenieur  en  chef  des  Mines :  Professeur  d'analyse  minerale  A  I'ecole  na- 
tionale  des  Mines,  Authorized  translation  by  A.  T.  Lincoln,  Ph.D.,  Assist- 
ant Professor  of  Chemistry,  Rensselaer  Polytechnic  Institute,  and  D.  H. 
Carnahan,  Ph.D.,  Associate  Professor  of  Romance  Languages,  University 
of  lUinois.     New  York,  1910.  Cloth,  8vo,  184  pages,  $1.75  net 

JONES.  Practical  Inorganic  Chemistry  for  Advanced  Students.  By 
Chapman  Jones,  F.I.C,  F.C.S.,  etc.    London,  1898.    Latest  reprint,  1906. 

Cloth,  i2>no,  23Q  pages,  $.60  net 

BASKERVILLE  &  CURTMAN.  Qualitative  Chemical  Analysis.  By 
Professor  CHARLES  BaSKERVILLE  and  Dr.  L.  J.  CUKTMAN,  College  of 
the  City  of  New  York.     New  York,  1910,        C/o/A,  8vo,  200 pages,  $1.40  net 

NOYES.  A  Detailed  Course  of  Qualitative  Chemical  Analysis  of  Inor- 
ganic Substances.  With  Explanatory  Notes  by  Arthur  A.  Noyes,  Ph.D. 
New  York,  1899.  Cloth,  8vo,  89  pages,  $1.25  net 

MORGAN.  Qualitative  Analysis,  As  a  laboratory  basis  for  the  study  of 
general  inorganic  chemistry.  By  William  Conger  Morgan,  Ph.D., 
Assistant  Professor  of  Chemistry  in  the  University  of  California.  New 
York,  1906,     Reprinted,  1907.  Cloth,  8vo,  351  pages,  $1.90  net 

HILLYER.  Laboratory  Manual.  Experiments  to  illustrate  the  elementary 
principles  of  chemistry.  By  H.  W,  HiLLYER,  Ph,D.,  Assistant  Professor 
of  Organic  Chemistry  in  the  University  of  Wisconsin.    New  York,  1900. 

Chtht  8vo,  200  pages,  $  .go  net 


A  List  of  Works  on  Chemistry — Continued 


ABEGG  &  HERZ.  Practical  Chemistry.  An  experimental  introduction  to 
laboratory  practice  and  qualitative  analysis  from  a  physiochemical  stand- 
point. By  R.  Abegg  and  W.  Herz.  Translated  by  H.  T.  Calvert,  B.Sc. 
London,  1901.  Cloth,  i2mo,  118  pages,  $1.50  net 

TALBOT.    An  Introductory  Course  of  Quantitative  Chemical  Analysis. 

With  explanatory  notes  and  stoichiometrical  probleTns.     By  H.  P.  Talbot, 
Ph.D.    New  York,  1908.    Fifth  Edition.    Rewritten  and  revised. 

Cloth,  8vo,  176  pages,  $1.50  net 

BAILEY.  Elements  of  Quantitative  Analysis.  By  G.  H.  Bailey,  D.Sc, 
Ph.D.     London,  1905.  Cloth,  i2mo,  246  pages,  $1.00  net 

LINCOLN  &  WALTON.  Exercises  in  Elementary  Quantitative  Chemi- 
cal Analysis  for  Students  of  Agriculture.  By  Azariah  Thomas 
Lincoln,  Ph.D.,  Assistant  Professor  of  Chemistry,  University  of  Illinois, 
and  James  Henri  Walton,  Jr.,  Ph.D.,  Assistant  Professor  of  Chemistry, 
University  of  Wisconsin.    New  York,  1907.    Third  reprint,  1910. 

Cloth,  8vo,  218  pages,  $1.50  net 

MILLER.  The  Calculations  of  Analjrtical  Chemistry.  By  Edmund  H. 
Miller,  Ph.D.,  Professor  of  Analytical  Chemistry  in  Columbia  University. 
New  York.     Third  Edition,  1906.  Cloth,  8vo,  201  pages,  $1.50  net 

WAD  DELL.  Arithmetic  of  Chemistry.  Being  a  simple  treatment  of  the 
subject  of  chemical  calculations.  By  JOHN  Waddell,  B.Sc,  Ph.D., 
D.Sc.    New  York,  1899.     Fifth  reprint,  1907. 

Cloth,  i2mo,  1 33  pages,  $  .go  net 

LUPTON.    Chemical  Arithmetic,  with  Twelve  Hundred  Examples.    By 

Sydney  Lupton,  M.S.,  F.C.S.    London,  1882.    Second  Edition,  1886. 
Sixth  reprint,  1907.  Cloth,  i6mo,  171  pages,  $  i.io  net 

GUIT^MAN.  Percentage  Tables  for  Elementary  Analysis.  By  Leo  F. 
Guttman,  Ph.D.     London,  1904.  Cloth,  8vo,  43  pages,  $1.10  net 

THORPE.  A  Series  of  Chemical  Problems,  with  Key  for  Use  in  Colleges 
and  Schools.  By  F.  E.  Thorpe,  LL.D.,  F.R.S.  Revised  and  enlarged 
by  W.  Tate,  Assoc.  N.S.S.,  F.C.S.  London,  1877.  Second  Edition,  1891. 
Latest  reprint,  1907.  Cloth,  i6mo,  13Q  pages,  $  .65  net 

HEMPEL.  Methods  of  Gas  Analysis.  By  Dr.  Walter  Hempel. 
Translated  from  the  third  German  edition  and  considerably  enlarged  by 
L.  M.  Dennis,  Professor  of  Analytical  and  Inorganic  Chemistry.  New 
York,  1902.    Latest  reprint,  1910.  Cloth,  i2mo,  487  pages _  $2.25  net 

WADE.  Introduction  to  the  Study  of  Organic  Chemistry.  A  theoreti- 
cal and  practical  textbook  for  students  in  the  universities  and  technical 
schools.    By  JOHN  Wade,  D.Sc.    London,  1897.     Second  Edition,  1905. 

Cloth,  i2mo,  646  pages,  $1.75  net 


PUBLISHED    BY 


THE  MACMILLAN  COMPANY 

64-66  Fifth  Avenue.  New  York 


A  List  of  Works  on  Chemistry — Continued 


GATTERMAN.  The  Practical  Methods  of  Organic  Chemistry.  By  Lud. 
WIG  GatTERMAN,  Ph.D.  Translated  by  William  B.  Schober,  Ph.D. 
Authorized  translation.  The  second  American  from  the  fourth  German 
edition.     New  York,  1896,  1901.    Sixth  reprint,  1910. 

Cloth,  8vo,  3S0  pages,  $1.60  net 

SHERMAN.  Methods  of  Organic  Analysis.  By  Henry  C.  Sherman, 
Ph.D.,  Adjunct  Professor  of  Analytical  Chemistry  in  Columbia  ^University. 
New  York,  1905.  Cloth,  8vo,  24 j  pages,  $1.75  net 

COHEN.  Theoretical  Organic  Chemistry.  By  Julius  B.  Cohen,  Ph.D., 
B.Sc.     London,  1902.     Latest  reprint,  1907. 

Cloth,  i2mo,  578  pages,  $1.50  net 

COHEN.  Practical  Organic  Chemistry  for  Advanced  Students.  By 
Julius  B.  Cohen,  Ph.D.,  B.Sc     London,  1900.    Second  Edition,  1908. 

Cloth,  i2mo,  4s6  pages,  $  .80  net 

LASSAR-COHEN.  A  Laboratory  Manual  of  Organic  Chemistry.  A 
compendium  of  laboratory  methods  for  the  use  of  chemists,  physicians,  and 
pharmacists.  By  Dr.  Lassar-Cohen.  Translated,  with  the  author's  sanc- 
tion, from  the  second  German  edition,  by  Alexander  Smith,  B.Sc,  Ph.D. 
London,  1895.    Reprinted,  1896.  Cloth,  8vo,  403  pages,  $2.25  net 

LACHMAN.  The  Spirit  of  Organic  Chemistry.  An  introduction  to  the 
current  literature  of  the  subject.  By  ARTHUR  Lachman,  Professor  of 
Chemistry  in  the  University  of  Oregon,  With  an  introduction  by  Paul  C. 
Greer,  M.D.,  Ph.D.,  Professor  of  General  Chemistry  in  the  University  of 
Michigan.    New  York,  1899.    Second  reprint,  1909. 

Cloth,  i2mo,  22Q  pages,  $1.50  net 

MANN.  Chemistry  of  the  Proteids.  By  Gustav  Mann,  M.D.,  B.Sc, 
University  Demonstrator  of  Physiology,  Oxford.    London,  1906. 

Cloth,  8'co,  606  pages,  $3.75  net 

LE  BLANC.  A  Textbook  of  Electro-Chemistry.  By  Max  Le  Blanc, 
Professor  in  the  University  of  Leipzig.  Translated  from  the  fourth  en- 
larged German  edition,  by  Willis  R.  Whitney,  Ph.D.,  Director  of  the  Re- 
search Laboratory  of  the  General  Electric  Company,  and  John  W.  Brown, 
Ph.D.,  Director  of  the  Research  and  Battery  Laboratory  of  the  National 
Carbon  Company.    New  York,  1907.    Reprinted,  1910. 

Cloth,  8vo,  335  pages,  $2.60  net 

BLOUNT.  Practical  Electro-Chemistry.  By  Bertram  Blount,  F.L.C., 
Assoc.  Inst.  C.E.     London,  1901.     Second  Edition.     Revised,  1906. 

Cloth,  8vo,  394  pages,  $3.25  net 

NEUMANN.  The  Theory  and  Practice  of  Electrolytic  Methods  of 
Analysis.  By  Dr.  Bernhard  Neumann.  Translated  by  John  B.  C. 
Kerslaw,  F.I.C.    London,  1878.  Cloth,  8vo,  254  pages,  $3.00  net 


A  List  of  Works  on  Chemistry — Continued 


TALBOT  &  BLANCHARD.  The  Electrolytic  Dissociation  Theory  with 
Some  of  its  Applications.  An  elementary  treatise  for  the  use  of  students 
of  chemistry.  By  HENRY  P.  Talbot,  Ph.D.,  Professor  of  Inorganic  and 
Analytical  Chemistry,  and  ARTHUR  A.  Blanchard,  Ph.D.,  Instructor  in 
Inorganic  Chemistry  at  the  Massachusetts  Institute  of  Technology.  Sec- 
ond Edition.     New  York,  1907.  Cloth,  85  pages,  $1.25  net 

JONES.  The  Theory  of  Electrolytic  Dissociation  and  Some  of  its  Appli- 
cations. By  Harry  C.  Jones,  Professor  of  Physical  Chemistry  in  the 
Johns  Hopkins  University.     New  York,  1900.     Third  Edition,  1906. 

Cloth,  8vo,  28Q  pages,  $1.60  net 

JONES.  Introduction  to  Physical  Chemistry.  By  H.  C.  Jones,  Professor 
of  Physical  Chemistry  in  the  Johns  Hopkins  University.     New  York,  1910. 

Cloth,  i2mo,  27 Q  pages,  $1.60  net 

JONES.  The  Elements  of  Physical  Chemistry.  By  H.  C.  Jones,  Profes- 
sor in  the  Johns  Hopkins  University.  Fourth  Edition.  Revised  and  en- 
larged.    New  York,  1909.  Cloth,  8vo,  650  pages,  $4.00  net 

WALKER.  Introduction  to  Physical  Chemistry.  By  James  Walker, 
D.Sc,  Ph.D.,  F.R.S.,  Professor  of  Chemistry  in  the  University  of  Edin- 
burgh.   London,  1899.    Fifth  Edition,  1909.    Reprinted,  1910. 

Cloth,  8vo,  38Q  pages,  $3.25  net 

REYCHLER.  Outlines  of  Physical  Chemistry.  By  A.  Reychler,  Pro- 
fessor of  Chemistry  in  the  University  of  Brussels.  Translated  from  the 
French,  with  the  author's  permission,  by  John  McCrae,  Ph.D.  London. 
Second  Edition,  1904.  Cloth,  i2mo,  268  pages,  $1.00  net 

BOYNTON.  Applications  of  the  Kinetic  Theory  to  Gases,  Vapors,  Pure 
Liquids,  and  the  Theory  of  Solutions.  By  William  Pingry  Boyn- 
TON,  Ph.D.,  Assistant  Professor  of  Physics  in  the  University  of  Oregon. 
New  York,  1904.  Cloth,  ismo,  288  pages,  $1.60  net 

THOMSON.    Application  of  D3mamics  to  Physics  and  Chemistry.    By 

Sir  J.  J.  THOMSON,  F.R.S.     London,  1888.      C/ot/i,  8vo,  312  pages,  $i.go  net 

HARDIN,    The  Rise  and  Development  of  the  Liquefaction  of  Gases. 

By  Willett  L.  Hardin,  Ph.D.     New  York.    Latest  reprint,  1905. 

Cloth,  i2mo,  250  pages,  $1.50  net 
TRAVERS.    The  Experimental  Study  of  Gases.     By  Dr.  Morris  W. 
Travers,  Assistant  Professor  of  Chemistry,  University  College,  London. 
With  Introduction  by  Sir  W.  Ramsay.    London,  1901. 

Cloth,  8vo,  323  pages,  $3.25  net 

RAMSAY.  The  Gases  of  the  Atmosphere;  The  History  of  their  Dis- 
covery. By  Sir  WiLLiAM  Ramsay,  K.C.B.,  F.R.S.  London,  1896. 
Third  Edition,  1905.  Cloth,  i2mo,  2q6  pages,  $2.00  net 

FLEISCHER.  A  System  of  Volumetric  Analysis.  By  Dr.  Emil  Fleis- 
cher. Translated,  with  notes  and  additions,  from  the  second  German 
edition,  by  M.  M.  Pattison  Muir,  F.R.S.E.,  Owens  College,  Manchester. 
London.  Cloth,  i2mo,  277  pages,  $2.00  net 


A  List  of  Works  on  Chemistry — Continued 

ROSCOE.  Spectnun  Analysis.  By  Sir  Henry  E.  Roscoe,  F.R.S.  Re- 
vised by  the  author  and  A,  Schuster,  F.R.S.     London. 

Cloth,  8vo,  colored  plates,  $6.00  net 

LANDAUER.  Blowpipe  Analysis.  By  J.  Landauer.  Authorized  Eng- 
lish edition  by  James  Taylor.     London,  1879.     Third  Edition,  1901. 

Cloth,  i2mo,  1/3  Pages,  $1.10  net 

GETMAN.  The  Elements  of  Blowpipe  Analysis.  By  Frederick  Hut- 
ton  Getman,  F.C.S.     New  York,  1899.     Cloth,  i2mo,  77  pages,  $  .60  net 

BEHRENS.  A  Manual  of  Microchemical  Analysis.  By  Professor  H. 
Behrens.  With  an  introductory  chapter  by  Professor  John  W.  Judd, 
F.R.S.    London,  1894.  Cloth,  i2mo,  246  pages,  $1.50  net 

ELSDEN.  Principles  of  Chemical  Gteology.  A  review  of  the  application 
of  the  equilibrium  theory  to  geological  problems.  By  James  Vincent 
Elsden,  D.Sc,  F.G.S.    London,  1910,        Cloth,  Svo,  222  pages,  $1.60  net 

TUTTON.  Crystalline  Structure  and  Chemical  Constitution.  By 
A.  E.  H.  Tutton,  D.Sc.,  M.A.,  F.R.S.,  etc.  Vice  President  of  the  Miner- 
alogical  Society,  etc.     London,  1910.  Cloth,  Svo,  204  pages,  $1.60  net 

MIERS.    Mineralogy:  An  Introduction  to  the  Scientific  Study  of  Min- 
erals.    By  H.  A.  MiERS,  D.Sc.,  M.A.,  F.R.S.,  Professor  of  Mineralogy  at 
Oxford.    London,  1902. 
Cloth,  Svo,  5S4  pages,  with  2  colored  plates  and  716  illustrations,  $8.00  net 

THORP.  Outlines  of  Industrial  Chemistry.  A  textbook  for  students. 
By  Frank  Hall  Thorp,  Ph.D.  Second  Edition,  revised  and  enlarged, 
and  including  a  chapter  on  Metallurgy,  by  Charles  D.  Demond,  S.B.  New 
York,  1905.    Latest  reprint,  1908.  Cloth,  Svo,  618  pages,  $3.75  net 

SCHNABEL.  Handbook  of  Metallurgy.  By  Dr.  Carl  Schnabel,  Konigl. 
Preuss.  Bergrath.  Professor  of  Metallurgy.  Translated  by  Henry  Louis, 
MA.,  A.R.S.M.,  F.I.C.,  etc.     Second  Edition.     London,  1907. 

Cloth,  Svo,  2  vols.,  pages  1123  and  S67,  per  vol.,  $6.50  net 

BAILEY.  A  Textbook  of  Sanitary  and  Applied  Chemistry  of  Water, 
Air,  and  Food.  By  E.  H.  S.  Bailey,  Ph.D.,  Professor  of  Chemistry. 
University  of  Kansas,     New  York,  1907.     Reprinted  1908,  1910. 

Cloth,  i2mo,  345  pages,  $1.40  net 

SNYDER.  The  Chemistry  of  Plant  and  Animal  Life.  By  Harry  Sny- 
der, B.S.,  Professor  of  Agricultural  Chemistrj',  University  of  Minnesota. 
New  York,  1903,     Fifth  reprint,  1910.         Cloth,  i2mo,  406  pages,  $1.25  net 

ARRHENIUS.  Immuno-Chemistry.  The  application  of  the  principles  of 
physical  chemistry  to  the  study  of  the  biological  antibodies.  By  SVANTE 
Arrhenius.    New  York,  1907.  Cloth,  i2mo,  30Q  pages,  $1.60  net 

SNYDER.  Dairy  Chemistry.  By  Harry  Snyder,  B.S..  Professor  of  Agri- 
cultural Chemistry,  University  of  Minnesota.  New  York,  1905.  Reprinted, 
1907*  Cloth,  i2mo,  I  go  pages,  $1.00  net 


A  List  of  Works  on  Chemistry — Continued 


BARTHEL.  Methods  used  in  the  Examination  of  Milk  and  Dairy  Prod 
nets.  By  Dr.  Chr.  Barthel,  Stockholm.  Translation  by  W.  Goodwin, 
M.Sc,  Ph.D.     London,  1910.  Cloth,  8vo,  260  pages,  $i.qo  net 

SNYDER.  Human  Foods  and  their  Nutritive  Value.  By  Harry  Sny- 
der, B.S.,  Professor  of  Agricultural  Chemistry,  University  of  Minnesota, 
and  Chemist  of  the  Minnesota  Experiment  Station.     New  York,  1909. 

Cloth,  i2mo,  362  pages,  $1.23  net 

ROLFE.  The  Polariscope  in  the  Chemical  Laboratory.  An  introduction 
to  polarimetry  and  related  methods.  By  George  William  Rolfe, 
A.M.,  Instructor  in  Sugar  Analysis  in  the  Massachusetts  Institute  of  Tech- 
nology.   New  York,  1905.  Cloth,  i2mo,  320  pages,  $i.po  net 

YOUNG.  Fractional  Distillation.  By  Sidney  Young,  D.Sc,  F.R.S.,  Pro- 
fessor of  Chemistry  in  University  College,  Bristol.     London,  1903. 

Cloth,  i2mo,  284  pages,  $2.60  net 

MELDOLA.  The  Chemistry  of  Photography.  By  Raphael  Meldola, 
F.R.S.,  etc.    London,  1899.     Latest  reprint,  1901. 

Cloth,  i2fno,  382  pages,  $2.00  net 

DERR.    Photography  for  Students   of  Physics   and  Chemistry.     By 

Louis  Derr,  M.A.,  S.B.,  Associate  Professor  of  Physics  in  the  Massachu- 
setts Institute  of  Technology.    New  York,  1906.    Reprinted,  1909. 

Cloth,  i2mo,  247  pages,  $1.40  net 

FRAPS.  Principles  of  Dyeing.  By  G.  S.  Fraps,  Ph.D.,  Assistant  Professor 
of  Chemistry,  North  Carolina  College  of  Agriculture  and  Mechanic  Arts. 
New  York,  1903.  Cloth,  i2mo,  270  pages,  $1.60  net 

SCHULTZ  &  JULIUS.  A  Systematic  Survey  of  the  Organic  Colouring 
Matters.  Founded  on  the  German  of  Drs.  G.  SCHULTZ  and  P.  JULius. 
Revised  throughout  and  greatly  enlarged  by  Arthur  G.  GREEN,  F.I.C., 
F.C.S.    London.  Cloth,  8vo,  2qo  pages,  $7.00  net 

LEWKOWITSCH.    Chemical  Technology  and  Analysis  of  Oils,  Fats, 
and  Waxes.    By  Dr.  J.  Lewkowitsch,  M.A.,  F.I.C.,  Consulting  Chem- 
ist to  the  city  and  guilds  of  London  Institute.    Fourth  Edition.    Entirely 
rewritten  and  enlarged.    3  vols.    London,  1909. 
Cloth,  8vo,  Vol.  I  542  pages.  Vol.  II  812  pages.  Vol.  Ill  406  pages,  $15.00  net 

LEWKOWITSCH.  Laboratory  Companion  to  Fats  and  Oils  Indus- 
tries.   By  Dr.  J.  Lewkowitsch,  M.A.,  F.I.C.    London,  1909. 

Cloth,  8vo,  IQ7  pages,  $i.qo  net 

GUTTMAN.  The  Manufacture  of  Explosives.  A  theoretical  and  practi- 
cal treatise  on  the  history,  the  physical  and  chemical  properties,  and  the 
manufacture  of  explosives.  By  Oscar  Guttman,  Assoc.  M.  Inst.  C.E., 
F.I.C.    In  two  volumes.    London,  1895. 

Cloth,  8vo,  Vol.  I  348  pages,  Vol.  II  444  pages,  the  set  $q.oo  net 


A  List  of  Works  on  Chemistry — Continued 


GUTTMAN.  The  Manufacture  of  Explosives.  Twenty  Years'  Progress. 
Four  Cantor  Lectures  delivered  at  the  Royal  Society  of  Arts  in  November 
and  December,  1908.  By  OsCAR  GuiTMAN,  member  of  Inst  of  Civil 
Engineers,  etc.    London,  1908.  Cloth,  8vo,  84  pages,  $1.10  net 

VON  MEYER.  A  History  of  Chemistry  from  Earliest  Times  to  the 
Present  Day.  Being  also  an  introduction  to  the  study  of  the  science.  By 
Ernst  von  Meyer,  Ph.D.  Translated  with  the  author's  sanction  by 
George  McGowan,  Ph.D.  Third  English  edition,  with  various  additions 
and  alterations.    London.    First  Edition,  1891.    Third  Edition,  1906. 

Cloth,  8vo,  691  pages,  $4.25  net 

THORPE.  Essays  in  Historical  Chemistry.  By  T.  E.  Thorpe,  C.B., 
LL.D.,  F.R.S.,  Principal  of  the  Government  Laboratory,  London.  Lon- 
don, 1902.  Cloth,  8vo,  582  pages,  $4.00  net 

THORPE.  Humphrey  Davy,  Poet  and  Philosopher.  By  T.  E.  Thorpe, 
LLP.,  F.R.S.    New  York,  1896.  Cloth,  i2mo,  240  pages,  $1.23  net 

SHENSTONE.    Justice  von  Liebig:  His  Life  and  Work  (1803-1873). 

By  W. .     Shenstone,  F.I.C,  Lecturer  on  Chemistry  in  Clifton  College. 
London,  1895.  Cloth,  i2mo,  21Q  pages,  $1.25  net 

ROSCOE.  John  Dalton,  and  the  Rise  of  Modern  Chemistry.  By  Sir 
Henry  E.  Roscoe,  D.C.L.,  LL.D.,  F.R.S.    London,  1895. 

Cloth,  i2tno,  212  pages,  $1.25  net 

ROSCOE  &  HARDEN.  A  New  View  of  the  Origin  of  Dalton's  Atomic 
Theory.  A  contribution  to  chemical  history.  Together  with  letters  and 
documents  concerning  the  life  and  labors  of  John  Dalton,  published  from 
manuscript  in  the  possession  of  the  Literary  and  Philosophical  Society  of 
Manchester.  By  Sir  HENRY  E.  RoscoE,  F.R.S.,  and  Arthur  Harden. 
London.  Cloth,  8vo,  $1.90  net 

JONES.  An  Introduction  to  the  Science  and  Practice  of  Qualitative 
Chemical  Analysis.  Inorganic.  By  Chapman  Jones,  F.I.C,  F.C.S.. 
etc    London,  1898.    Reprinted,  1906.      Cloth,  i2mo,  213  pages,  $  .60  net 


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